Musannaf Ibn Abi Shayba 3:3764

Asbat ibn Muhammad narrated to us, from Mutarrif, from Sulayman ibn Buzay', who said: I entered upon Salim while he was praying sitting down. He made his standing position cross-legged. When he wanted to bow, he bowed while he was cross-legged. And when he wanted to prostrate, he folded his leg.