Musannaf Ibn Abi Shayba 3:4015

Waki’ narrated to us, he said: ‘Isa al-Khayyat narrated to us, he said: I heard Sa’id ibn al-Musayyib saying: What is the matter with one of you, when he has prayed the two rak’ahs, that he rolls his hands [in the dust] upon the taslim?