Shaykh Muhammad ibn Uthaymeen (may Allaah have mercy on him) said: It was proven in al-Saheehayn that Ibn Abbaas (may Allaah be pleased with him) said: The people were commanded that the last thing they should do in Makkah was to circumambulate the Ka'bah, but an exception was made for menstruating women. Narrated by al-Bukhaari, 1755; Muslim, 1328.
So tawaaf should be the last action of Hajj that a person does.
People make several mistakes when performing the farewell tawaaf:
Some people do not make tawaaf the last thing that they do, rather they go down to Makkah and do the farewell tawaaf when they still have to stone the jamaraat, then they go out to Mina and stone the jamaraat and then leave. This is a mistake and that does not suffice as the farewell tawaaf in this case, because it is not the last thing that the person does in Makkah, rather the last thing that he does is stoning the jamaraat.
Some people do the farewell tawaaf and then stay in Makkah after that. This means that their farewell tawaaf is invalidated, and they must do another one when they are going to leave. But if a person stays in Makkah after doing the farewell tawaaf in order to buy something or to load his luggage etc, there is nothing wrong with that.
Some people, when they do the farewell tawaaf and want to leave the Mosque, walk backwards, saying that they do not want to turn their backs to the Ka'bah. This is a bid'ah (innovation) which was not done by the Messenger of Allaah (peace and blessings of Allaah be upon him) or by any of his companions. The Messenger of Allaah (peace and blessings of Allaah be upon him) venerated Allaah and His House and if this were indeed an act of veneration towards Allaah and His House, the Prophet (peace and blessings of Allaah be upon him) would have done it. The Sunnah is, when a person has completed the farewell tawaaf, to leave the Mosque walking forwards, even if he turns his back towards the Ka'bah in this situation.
Some people, after doing the farewell tawaaf, stop at the door when leaving the mosque and turn to face the Ka'bah, as if bidding farewell to it, and they make du'aa' or say salaams and so on. This is also a kind of bid'ah, because the Prophet (peace and blessings of Allaah be upon him) did not do that. If it were something good the Prophet (peace and blessings of Allaah be upon him) would have done it.
Reproduced from Islam QA