Musnad Ahmad 1159:7

'Abd al-Razzaq narrated to us, Malik narrated to us, from 'Abd Allah ibn Abi Bakr, from Humayd ibn Nafi', that Zaynab bint Abi Salamah informed him that she entered upon Umm Habibah bint Abi Sufyan, and she said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "It is not lawful for a woman who believes in Allah and the Last Day to mourn for a dead person for more than three nights, except for a husband, [for whom she mourns] four months and ten [days]." Abu 'Abd al-Rahman said: My father said: "Humayd ibn Nafi' is Abu Aflah, and he is Humayd Safira."