Musnad Ahmad 32:1860

Ali ibn Ishaq narrated to us, Abdullah and Attab informed us, they said: Abdullah narrated to us, he said: Salam ibn Abi Muti’ informed us, from Ayyub, from Abu Qilabah, from Abdullah, the foster-son of Aisha, from Aisha, from the Prophet, peace and blessings of Allah be upon him, who said: "There is no deceased person upon whom a community of people from the Muslims prays, reaching the number of one hundred, and they intercede for him, but that they are granted intercession for him." Salam said: So I narrated it to Shu’bah ibn al-Habhab, and he said: Anas ibn Malik narrated it to me, from the Prophet, peace and blessings of Allah be upon him.