The Sunnah is what has been established from the Prophet (may Allah's peace and blessings be on him) of his sayings, actions or tacit approvals.
The basic principle with regards to his sayings is that they are for legislation. This is because he is conveying (this message) on behalf of His Lord, and he was sent as a guide for the creation, and he was ordered to inform and clarify matters for the people, as Allah says (what means): And We revealed to you the message that you may make clear to the people what was sent down to them (16:44) and He said (what means): O Messenger, announce that which has been revealed to you from your Lord, and if you do not, then you have not conveyed His message. (5:67)
The proof for this general principle (that the words of the Prophet - may Allah's peace and blessings be upon him - are considered to be legislation) is the hadeeth reported by Abu Dawud (3646): Abdullah ibn Amr said: I used to write everything I heard from the Messenger of Allah (may Allah's peace and blessing be upon him), wanting to memorize it but Quraysh forbade me saying: do you write everything you hear while the Messenger of Allah (may Allah's peace and blessings be upon him) is a human being who speaks when angry and when pleased?' So I abstained from writing and mentioned that to the Messenger of Allah (may Allah's peace and blessings be upon him) and he pointed to his mouth with his finger and said: Write, for by the One in whose hand my soul rests, nothing but truth comes from it.'
There were times when he (may Allah's peace and blessings be upon him) said something and it was not mean to be legislation; however, this was other than the norm and there is evidence indicating that this was the case. One example is that of the famous story about pollinating date palms.
As for the actions of the Prophet of Allah (may Allah's peace and blessing be upon him), they fall into four categories. First, there are those actions which were for the sake of legislation. Secondly, there are those actions which were natural and habitual actions which conform with being human. There were also those actions which wavered between being habit/ custom and being legislation. Finally, there were certain actions which were specific to him (may Allah's peace and blessings be upon him).
Al Imam al Bukhari prefaced the chapter The Book of Adherence in his book, as-Saheeh, with the sub-heading of Section on Imitating the Actions of the Prophet (may Allah's peace and blessings be upon him)'
Al Hafidh ibn Hajar (may Allah have mercy on him) said in his commentary:
The basis of this is the (meaning of the) saying of the Exalted: There has certainly been for you in the Messenger of Allah an excellent pattern (33:21)
A group (of scholars) have said that it is an obligation (to imitate the Prophet) because it is covered in the general command found in the (meaning of the) saying of the Exalted: And whatever the Messenger has given you - take (59:7) and (the meaning of) His saying: then follow me, [so] Allah will love you (3:31) and (the meaning of) His saying: so follow him. Therefore, it is necessary (obligatory) to follow him in his actions, just as it is to follow his sayings unless an evidence establishes that it is recommended or specific to the Prophet.
Others said: It carries the possibility of being obligatory, encouraged or permitted and so corroborating evidence is required.
The majority opine that it (actions) is encouraged if the aspect of worship is apparent. And it was said even if it is not apparent (i.e. the aspect of worship). Others distinguished between that which is repetitive and that which is not.
Others said: If what he (may Allah's peace and blessings be upon him) does is clarification of a general concept, then it takes the same ruling as the general concept, either obligatory, encouraged or allowed. If the aspect of worship is apparent, then it is encouraged, and if no aspect of worship is apparent, then it is permitted. As for his tacit approval of things which are done in his presence, then that indicates permissibility. The issue is elaborated on in the principles of jurisprudence. End of quote from Fath al Bari (13/ 288-289).
From the examples of what is for legislation: The actions of Wudhu (ablution), Salah (formal prayers), and Hajj (pilgrimage). It is known that they are for legislation from different angles:
First: They are clarification for something commanded, either obligatory or encouraged, such as the actions of wudhu for they are clarification of the (meanings of the) saying of the Exalted: O you who have believed, when you rise to [perform] prayer, wash your faces and your forearms to the elbows and wipe over your heads and wash your feet to the ankles. (5:6)
Second: There is an open call to imitate and follow as in his (may Allah's peace and blessing be upon him) saying: Pray as you have seen me pray, or his saying Take your rites (of Hajj) from me.
Third: Incitement towards doing the action while doing it himself, so in this case the sunnah of word and action are combined.
The gauge for customary practices is: Everything that is done by human nature and there is no apparent intent of worship or legislation or invitation to imitate in it such as; standing and sitting, eating and drinking, sleeping, taking shade, walking, combing hair and the lengthening or shortening of it, the wearing of a waist wrapper, (upper) body cover, shirt (robe) or turban because people must wear garments and the Prophet (may Allah's peace and blessings be upon him) wore these garments which existed among his people.
As for what may possibly be from customary practices or for legislation, then its gauge is: It is done by human nature, but it occurred along with an act of worship, either a part of it or a means towards it as in riding for Hajj or entering Makkah from Kada or his (may Allah's peace and blessing be upon him) stopping in al Muhassab after Hajj (which is the name of a place between Makkah and Mina, although closer to Mina and it is also known as al Abtah). The Companions differed over this stopping as to whether it was for legislation or not. Abdullah ibn Umar (may Allah be pleased with them both) saw that it was sunnah while Abdullah ibn Abbas (may Allah be pleased with them both) used to say that at-Tahseeb (stopping in al Muhassab) was nothing. It was merely a place where the Messenger of Allah (may Allah's peace and blessings be upon him) stopped. Aishah (may Allah be pleased with her) agreed with ibn Abbas and said: Stopping al Abtah is not sunnah. The Messenger of Allah (may Allah's peace and blessings be upon him) only stopped there because it would have been easier for him to leave when he left. See: Saheeh al Bukhari (1765, 1766) and Saheeh Muslim (1310).
So whatever carries the possibility of being either from customary practices or for legislation, will either be encouraged or permitted.
As for that which is purely customary practice, then it is permitted/ allowed, and if one were to follow it then there is no blame on him for Abdullah ibn Umar (may Allah be pleased with him) used to wear (cow) leather sandals and dye his hair with sufrah (a yellowish colour). When asked about it he said: As for the leather sandals, I saw the Messenger of Allah (may the peace and blessings of Allah be upon him) wear sandals which had no hair (fur) on them and took ablution with them on so I like to wear them. As for the sufrah (yellowish dye), then I saw the Messenger of Allah (may Allah's peace and blessing be upon him) dyeing with it and I like to dye with it. Related by al Bukhari 1/267, number 166
And it has been reported that al Imam ash-Shafi'ee said to some of his companions: Give me water, and he drank standing for the Prophet (may Allah's peace and blessing be upon him) drank standing.
And it is reported from al Imam Ahmad that he left by night and disappeared for three days then moved on to another place, following the example of the Prophet (may Allah's peace and blessings be upon him) for he travelled by night and hid in the cave for three days and he said: No hadeeth reached me except that I acted upon it, even giving the cupper a dinar.
See: Ma'alim Usool al Fiqh inda Ahl as-Sunnah wa al Jama'ah, Dr Muhammad Husein al Jizani, pg 128 and Tayseer Usool al Fiqh, by Abdullah ibn Yusuf al Judayy'I (121-124).
There is no harm in imitating these customary practices, unless it is completely contrary to the customs of your people - for example, wearing the waste wrapper (izar) and upper body cover (rida) in a community which does not wear them; wearing a turban amongst people who are not accustomed to it; or keeping one's hair long if it is known to be a sign of the corrupt or criminals. In that case, one should leave it due to what is in it of seeking fame (deliberately trying to stand out and attract attention), or imitating those whom we have been ordered to differ from.
Al Hafidh ibn Hajar (may Allah have mercy on him) said while speaking on dyeing (hair), that is: with henna. The difference among the pious predecessors regarding it:
Dyeing (hair) in general is most befitting as by way of it one fulfils the obligation of differing from the People of the Book, and one protects his hair from having dust and other things sticking to it, unless it is customary for the people of the land to leave off dyeing and the one amongst them who does it alone becomes known (stands out) due to it. In that case, leaving it is better. End quote from Fath al Bari (10/367-368)
A group of scholars have stated this with regards to the two issues of wearing a turban and lengthening the hair as previously clarified in question 113894 and question 69822.
And Allah knows best.
Reproduced from Islam QA