From Sahih Muslim (Hadith 2189):
Abu Huraira reported Allah's Messenger (ﷺ) as saying:He who attends the funeral till the prayer is offered for (the dead), for him is the reward of one qirat, and he who attends (and stays) till he is buried, for him is the reward of two qirats. It was said: What are the qirats? He said: They are equivalent to two huge mountains. Two other narrators added: Ibn 'Umar used to pray and then depart (without waiting for the burial of the dead). When the tradition of Abu Huraira reached him, he said:" We have lost many qirats
Reference: Muslim 2189