Is Moustache Prohibited in Islam?
Question

Some Brothers of mine are growing their beards but they are shaving their moustaches. They are saying that Omar, may Allah be pleased with him, did this and so it is good to do it. I read some answers on your website regarding the trimming of the moustaches, but it is permissible to shave it.
Praise be to Allah.The scholars differed concerning the recommended Sunnah regarding the moustache, and there are two views:

The first view is that it is Sunnah to shave off the moustache altogether. This is the view of the Hanafis and Hanbalis. They quoted as evidence the apparent meaning of the words of the Prophet (peace and blessings of Allah be upon him) that were narrated concerning this, such as “Trim the moustache” [Narrated by Al-Bukhari, 5892 and Muslim, 259] and other similar reports in Al-Bukhari and Muslim.

At-Tahawi (may Allah have mercy on him) said in Sharh Ma`ani Al-Athar (4/230):
Shaving the moustache is better than trimming. This is the view of Abu Hanifah, Abu Yusuf and Muhammad (may Allah have mercy on them). (End quote)
Ibn `Abidin (may Allah have mercy on him) narrated in Radd Al-Muhtar (2/550) that later scholars preferred to trim it and said:
The (Hanafi) view according to some later scholars among our Shaykhs is that the moustache should be trimmed. It says in Al-Bada’i`: This is the correct view. (End quote)

The second view is that the Sunnah is to trim the moustache, and that shaving it is disliked. This is the view of the Malikis and Shafi`is. Imam Malik (may Allah have mercy on him) was very strict concerning that.

They quoted the following as evidence:

It was narrated from Abu Hurayrah (may Allah be pleased with him) that he heard the Prophet (peace and blessings of Allah be upon him) say: “The Fitrah is five things: circumcision, shaving the pubes, trimming the moustache, trimming the nails and plucking the armpit hairs.” (Narrated by Al-Bukhari,  5891 and Muslim, 257)
It was narrated that Al-Mughirah ibn Shu`bah (may Allah be pleased with him) said: “My moustache grew too long and the Prophet (peace and blessings of Allah be upon him) trimmed it for me on a Siwak.” (Narrated by Abu Dawud, 188; classed as authentic by Al-Albani in Sahih Abu Dawud)

Al-Bayhaqi (may Allah have mercy on him) narrated in As-Sunan Al-Kubra (1/151) with his chain of narration that `Abd Al-`Aziz ibn `Abdullah Al-Uwaysi said: Malik ibn Anas mentioned that some people shave their moustaches, and he said: The one who does that should be beaten. The Hadith of the Prophet (peace and blessings of Allah be upon him) about the moustache does not speak of shaving, rather it should be trimmed just enough to let the edge of the lips and the mouth show.
Malik ibn Anas (may Allah have mercy on him) said: Shaving the moustache is a Bid`ah (innovation) that has appeared among the people. (End quote)
Abul-Walid Al-Baji (may Allah have mercy on him) said in Al-Muntaqa Sharh Al-Muwatta` (7/266):
Ibn `Abd Al-Hakam narrated from Malik: Trimming the moustache does not mean shaving it. I think that the one who shaves his moustache should be disciplined. Ashhab ibn Malik narrated: Shaving it is a Bid`ah (innovation).
Malik (may Allah have mercy on him) said: It was narrated from `Umar ibn Al-Khattab (may Allah be pleased with him) that when he was upset by something, he would twist his moustache. If it was shaved off, there would be nothing to twist. (End quote from At-Tamhid, 21/62-68).
An-Nawawi (may Allah have mercy on him) said in Al-Majmu` (1/34-341):
The guideline on trimming the moustache is that it should be trimmed so that the edge of the lip can be seen, but it should not be shaved off completely. This is our view. End quote.
In Nihayat Al-Muhtaj by Ar-Ramli (8/148), who is one of the Shafi`i Imams, it says: It is disliked to shave the moustache. (End quote)
This opinion was also narrated from a number of the Salaf.
Al-Bayhaqi (may Allah have mercy on him) narrated in As-Sunan Al-Kubra (1/151) with his chain of narrators that Shurahbil ibn Muslim Al-Khawlani said: I saw five of the companions of the Messenger of Allah (peace and blessings of Allah be upon him) trimming their moustaches and letting their beards grow and dyeing them with saffron: Abu Umamah Al-Bahili, `Abdullah ibn Bisr, `Utbah ibn `Abd Al-Sulami, Al-Hajjaj ibn `Amir Ath-Thamali and Al-Miqdam ibn Ma`di Yakrib Al-Kindi. They used to trim their moustaches to the edge of the lip.
They responded to the evidence quoted in favour of the first view in two ways:

What is meant by trimming is trimming the edge of the hair which grows over the lip, not shaving off the hair completely, based on the evidence of the reports which mention trimming only.

Abul-Walid Al-Baji (may Allah have mercy on him) said in Al-Muntaqa Sharh Al-Muwatta` (7/266):
Ibn Al-Qasim (may Allah have mercy on him) narrated from Malik that the explanation of the Hadith of the Prophet (peace and blessings of Allah be upon him) about trimming the moustache is that it is to be trimmed enough to let the red part of the lips show and the edges of the mouth. (End quote)
An-Nawawi (may Allah have mercy on him) said in Al-Majmu` (1/340):
These reports – i.e. the reports which speak of trimming the moustache – are understood by us to mean trimming it to the edge of the lips, not shaving it off completely. End quote.

Trimming does not mean removing it altogether, rather it means removing part of it.

The more correct view – and Allah knows best – is the second one, which is that the Sunnah is to trim the moustache and not to shave it.
Shaykh Ibn `Uthaymin (may Allah have mercy on him) said in Majmu` Al-Fatawa (11/Bab Al-Siwak wa Sunan Al-Fitrah/question no. 54):
The best is to trim the moustache as is the Sunnah. As for shaving it, that is not Sunnah. The analogy drawn by some scholars, that it is prescribed to shave it as the head is shaved in Hajj is an analogy when a clear text states something else, so this analogy does not carry any weight. Hence Malik said concerning shaving the moustache: It is an innovation that has appeared among the people, but we should not turn away from what is mentioned in the Sunnah, because following it is guidance, righteousness, happiness and success. (End quote)
The Standing Committee for Issuing Fatwas was asked: In a number of Hadiths it says “trim the moustache”. Is shaving different from trimming? Some people trim the first part of the moustache that is closest to the upper lip, and they leave the hair of the moustache, so they trim nearly half of the moustache and leave the rest. Is this what is meant? Or does trimming the moustache mean shaving off all of it? Please advise me of the manner in which the moustache should be trimmed.
They replied:
The authentic Hadiths from the Messenger of Allah (peace and blessings of Allah be upon him) indicate that it is prescribed to trim the moustache. For example, the Prophet (peace and blessings of Allah be upon him) said: “Trim the moustache and let the beard grow; be different from the Mushrikin.” (Narrated by Al-Bukhari and Muslim)
And he (peace and blessings of Allah be upon him) said: “Trim the moustache and let the beard grow; be different from the Magians,” and in some versions it says: “Trim the moustache.” Trimming means cutting it very short. The one who cuts his moustache very short so that the upper lip is visible or trims it is not to blame, because the Hadiths mention two things, but it is not permissible to leave the edges of the moustache, rather the whole moustache should be trimmed or cut, in accordance with the Sunnah. (End quote from Fatawa Al-Lajnah Al-Da`imah, 5/149)
Shaykh `Abd Al-`Aziz ibn Baz, Shaykh `Abd Al-Razzaq `Afifi, Shaykh `Abdullah ibn Qa`ud.
At-Tabari and Al-Qadi `Iyad favoured the view that both are permissible: shaving and trimming; Al-Hafidh Ibn Hajar also inclined towards this view in Fat-h Al-Bari (10/347). (Al-Mawsu`ah Al-Fiqhiyyah, 25/320)
And Allah knows best