Musannaf Ibn Abi Shayba 3:1694

Muhammad ibn Fudayl narrated to us, from ‘Ata’ ibn al-Sa’ib, from Abu ‘Abd al-Rahman, who said: A man from the companions of the Prophet (may Allah bless him and grant him peace) narrated to us that the Messenger of Allah (may Allah bless him and grant him peace) said: "When one of you prays and completes his prayer, then sits in his place of prayer remembering Allah, he is in a state of prayer. And the angels pray for him, saying: 'O Allah, have mercy on him and forgive him.' And if he enters his place of prayer waiting [for the next prayer], it is like that."