Praise be to Allaah.
It is well established that the names and attributes of Allah are a matter that is limited to what is mentioned in the Qur'aan and Sunnah, i.e., they can only be known from the Islamic texts that mentioned them, and there is no room in this matter for ijtihaad or qiyaas (analogy) or istihsaan (personal view).
Imam Ahmad (may Allah have mercy on him) said: Allah cannot be described except in the terms in which He described Himself or His Messenger described Him, and that cannot go beyond what is mentioned in the Qur'aan and hadeeth.
End quote from Majmoo al-Fataawa, 5/26
Al-Khaazin said in his Tafseer (3/136):
The words of Allah (interpretation of the meaning): so call on Him by them [Ghaafir 40:65] means: call upon Allah by His names by which He called Himself or His Messenger called him. This indicates that the names of Allah, may He be exalted, are are matter to be based solely on the texts of the Qur'aan and saheeh hadeeths with no room for human opinion. What indicates that this opinion is correct and supports it is the fact that it is permissible to say Ya Jawaad but it is not permissible to say Ya Sakhi (even though both mean the same, i.e. Generous); and it is permissible to say Ya Aalim but it is not permissible to say Ya Aaqil (even though both mean knowing). End quote.
Any names or attributes of Allah that are not mentioned in the Qur'aan or Sunnah cannot be known by any means, because knowledge of the names and attributes of Allah is restricted to what is mentioned in them (the Qur'aan and Sunnah), and whatever we have no knowledge of, we leave the knowledge thereof to the One Who knows it, as in the duaa' for relief from distress: â€¦ as'aluka bi kulli ismin huwa laka sammayta bihi nafsaka aw anzaltahu fi kitaabika aw allamtahu ahadan min khalqika aw ista'tharta bihi fi ilm il-ghaybi andaka â€¦ (â€¦ I ask You by every Name belonging to You which You named Yourself with, or revealed in Your Book, or You taught to any of Your creation, or You have preserved in the knowledge of the unseen with Youâ€¦). Narrated by Ahmad, 3704; classed as saheeh by al-Albaani in al-Saheehah, 199
Ibn al-Qayyim (may Allah have mercy on him) said:
This indicates that Allah, may He be glorified and exalted, has names and attributes that He has preserved in the knowledge of the unseen with Him to the exclusion of His creation; they are not known to any angel who is close to Him or any Prophet who was sent. It is sufficient for us to admit our helplessness and stop at the limit of what has been permitted to us concerning that. So we should neither go to extremes concerning it nor ignore the issue altogether. End quote.
Badaa'i al-Fawaa'id, 2/413
Thus it becomes clear that ascribing to Allah the name mentioned, Zaahir, or any other name that is not mentioned in an Islamic text, is overstepping the permitted limit and speaking about Allah, may He be exalted, without knowledge.
Shaykh Ibn Uthaymeen (may Allah have mercy on him) said:
It is not permissible to ascribe any name or attribute to Allah, may He be exalted, that is not mentioned in the Qur'aan or Sunnah, because that is speaking about Allah, may He be exalted, without knowledge, and Allah says (interpretation of the meaning):
Say (O Muhammad SAW): (But) the things that my Lord has indeed forbidden are Al-FawÃ¢hish (great evil sins, every kind of unlawful sexual intercourse,) whether committed openly or secretly, sins (of all kinds), unrighteous oppression, joining partners (in worship) with AllÃ¢h for which He has given no authority, and saying things about AllÃ¢h of which you have no knowledge
[al-A raaf 7:33]
And follow not (O man i.e., say not, or do not or witness not) that of which you have no knowledge. Verily! The hearing, and the sight, and the heart, of each of those one will be questioned (by Allah)
End quote from Majmoo Fataawa wa Rasaa'il Ibn Uthaymeen, 4/230
And Allah knows best
For more information please see the answer to question no. 48964.