Mawlid al-Nabi, the observance of Muhammad's birth, falls on the twelfth of Rabi al-Awwal by the Sunni reckoning this rule records, while many Shia communities keep the same occasion on Rabi al-Awwal seventeen instead, a date that in Twelver Shia tradition also carries the birth of the sixth Imam, Jafar al-Sadiq, so the later date lets the two births be marked together. Neither date rests on an explicit early source fixing the day with certainty, and the difference reflects distinct transmitted traditions within each branch rather than a shared date read two ways.
The feast itself has been genuinely contested rather than universally embraced. Public Mawlid celebrations, with processions, devotional poetry and communal feasting, became widespread across much of the Sunni world from the medieval period onward, particularly associated with Sufi orders and popular practice in North Africa and South Asia. Conservative reform movements, most visibly the Wahhabi tradition centered in Saudi Arabia, have long argued that celebrating a birthday with fixed annual ritual has no basis in the practice of Muhammad's own generation and counts as an unwelcome innovation, so the same date that much of the Muslim world marks festively is, in some communities, not observed at all.