Musannaf Ibn Abi Shayba 3:1688

Jarir narrated to us, from Mansur, from Ibrahim, who said: It used to be said: If a man prays and then sits in his place of prayer, he is in a state of prayer, and the angels pray for him as long as he does not commit a hadath (ritual impurity) in it. If he sits in the mosque, he is in a state of prayer as long as he does not commit a hadath, and as long as he does not cause harm in it.