Hadithcore
Musnad Ahmad 4080
graded

It was narrated from Ibn Sireen that

Anas bin Malik attended the funeral of a man among the Ansar. They started to pray out loud for forgiveness for him, and Anas did not disapprove of that. Hushaim said: Khalid said in his hadeeth: And they put him into the grave from the end of the grave. And on one occasion Hushaim said: A man among the Ansar died in Basrah, and Anas bin Malik attended his funeral, and they prayed out loud for forgiveness for him.

References1 variant
Arabic/English book
Book 26, Hadith 4080