Abu Dawud Book 14, Hadith Number 3187.

Narated By Abdullah Ibn Abbas AbuSa’id al-Khudri AbuQatadah AbuHurayrah : Yahya ibn Subayh said: Ammar client of al-Harith ibn Nawfal told me that he attended the funeral of Umm Kulthum, and her son. The body of the boy was placed near the imam. I objected to it. Among the people there were Ibn Abbas, AbuSa’id al-Khudri, AbuQatadah and AbuHurayrah. They said: This is the sunnah (established practice of the Prophet).