Celebrating Mawlid al-Nabi (Muhammad’s Birthday): Allowed?
Question

Why do some people accept and somenot accept the celebration of Prophet Muhamamd’s birthday (malwid al-nabi)? What is your opinion?
Praise be to Allah.Is it permissible to celebrate Mawlid al-Nabi (Prophet Muhammad’s birthday)?
There is nothing in the Quran to say that we should celebrate the Mawlid al-Nabi or the birthday of the Prophet Muhammad (peace and blessings of Allah be upon him). The Prophet himself did not do this or command anyone to do it, either during his lifetime or after his death. 
Indeed, he told his Companions not to exaggerate about him as the Christians had exaggerated about Jesus (upon whom be peace). He said: “Do not exaggerate about me as the Christians exaggerated about the son of Maryam. I am only a slave, so say, ‘The slave of Allah and His Messenger.’” (Reported by al-Bukhari)
What did Prophet Muhammad do on the day of his birth?
What has been reported is that the Prophet (peace and blessings of Allah be upon him) made the day of his birth a day of worship, which is different to celebration. He was asked about fasting on Mondays, and he said: “That is the day on which I was born and the day on which I was entrusted with the Mission or when I was first given Revelation.” (Reported by Muslim, al-Nasai and Abu Dawood)
Did the Companions celebrate Mawlid al-Nabi?
Moreover, we know that the Sahabah (may Allah be pleased with them) were the people who loved the Prophet (peace and blessings be upon him) most. 
Was it reported that Abu Bakr (may Allah be pleased with him), who was the closest of people to him and the one who loved him the most, celebrated the birthday of the Prophet (peace and blessings of Allah be upon him)? 
Was it reported that ‘Umar (may Allah be pleased with him), who ruled for twelve years, or ‘Uthman (may Allah be pleased with him), did this?
Was it reported that ‘Ali (may Allah be pleased with him), his relative and foster son, did this? 
Was it reported that any of the Sahabah (may Allah be pleased with them) did this?
No, by Allah! Is it because they were not aware of its importance, or did they not truly love the Prophet (peace and blessings of Allah be upon him)? 
No one would say such a thing except one who has gone astray and is leading others astray.
Did leading Muslim scholars celebrate Mawlid al-Nabi?
Did any of the imams – Abu Haneefah, Malik, al-Shafi'i, Ahmad, al-Hasan al-Basri, Ibn Seereen (may Allah have mercy on them) – do this or command others to do it or say that it was good? By Allah, no! It was not even mentioned during the first and best three centuries. 
The Prophet (peace and blessings of Allah be upon him) said in a saheeh hadeeth: “The best of mankind are my generation (or my century), then those who come after them, then those who come after them. Then there will come a people who will not care if their testimony comes before their oath or vice versa (i.e., they will not take such a matter seriously).” (Reported by al-Bukhari, Muslim and al-Tirmidhi). 
When did the celebration of Mawlid al-Nabi appear?
The celebration of the Prophet’s birthday appeared many centuries later, when many of the features of true religion had vanished and bid’ah had become widespread.
Thus this celebration became a sign of one’s love for the Prophet (peace and blessings of Allah be upon him)? But can it be possible that the Sahabah, the imams and the people of the best three centuries were unaware of it, and it was only those who came later who were aware of its importance?! 
How to express love for Prophet Muhammad
What the Quran tells us is that love of the Prophet (peace and blessings of Allah be upon him) is demonstrated by following the guidance he brought. Allah says (interpretation of the meaning):
“Say (O Muhammad): ‘If you (really) love Allaah, then follow me, Allah will love you and forgive you your sins. And Allah is Oft-Forgiving, Most Merciful.
Say: ‘Obey Allah and the Messenger.’ But if they turn away, then Allah does not like the disbelievers.” [Aal ‘Imran 3:31-32]
The first ayah explains that love is just a claim, but the proof of sincerity is following what the Prophet (peace and blessings of Allah be upon him) brought. The second ayah reaffirms the importance and necessity of obeying Allah and His Messenger. 
Hence Allah ended the ayah with a very stern warning in which those who refuse to obey are described as kafirs, and Allah does not love the disbelievers. We ask Allah to keep us safe from that. 
The Prophet (peace and blessings of Allah be upon him) told us of the danger of not obeying him, and the danger of adding to what he brought. The celebration of Mawlid or his birthday is indeed an addition to what he brought – as all the scholars agree. He said: “The best of speech is the Book of Allah, and the best of guidance is the guidance of Muhammad. The most evil of things are those which are newly-invented (in religion), and every innovation is a going astray.” (Reported by Muslim and al-Nasai).
We ask Allah to protect us from bid’ah and to bless us by helping us to follow.
Allah knows best. May Allah bless our Prophet Muhammad.
And Allah knows best.