Why did Allah not grant the dua of the Prophet (peace be on him) for his ummah to be united?
Sa’d bin Abi Waqqas (may Allah be pleased with him) narrated that one day Allah’s Messenger (peace be on him) came from Al-‘Aliyah: a high place in Madinah. He passed by the mosque of Banu Mu’awiyah, went in and observed two rak’ahs there and we also observed prayer along with him (peace be upon him)…
