Q.The individual is asking about the Prophet (sallaahu alahyi wa sallam), did He fast on his birthday?
A. The shaykh said the Prophet (Sallaahu alayhi wa sallam) did not mention that he fasts because of his birthday. The Prophet (Sallaahu alayhi wa sallam) mentioned he fasts on Mondays and Thursdays, because these are two of the days on which actions are bought and presented to Allaah azza wa ja’al and the Thursday because it’s the day before the E’ed/ a day of gathering for the muslims. There is no doubt, we should understand that the Prophet (Sallaahu alayhi wa sallam) his birth was good for the humans. He was the individual Prophet Eesa (alayhi salaam) or Jesus gave glad tidings of, when Eesa (alayhi salaam) said I am giving you glad tidings of an individual who will come after & his name is Ahmed. Meaning the Prophet Muhammad (Sallaahu alayhi wa sallam). Likewise with the birth of the Prophet (Sallaahu alayhi wa sallam) the supplication of Ibraheem (alayhi sallam) was answered. Ibraheem (alayhi salaam) made a supplication that they would be from amongst his offspring a Prophet or a Messenger in Makkah. So there is no doubt that the birth of the Prophet (Sallahu alayhi wa sallam) bought much blessing to the world. However, the reason why the Prophet (Sallaahu alayhi wa sallam) fasted was because this was one of the days actions are bought up to Allaah and presented to Allaah. And that is on Mondays and Thursdays.
Shaykh Saalih ibn Muhammad al-Luhaydaan (May Allaah preserve him) (Kitaab-ut-Tawheed Class 01.12.12) Riyadh.