Musannaf Ibn Abi Shayba 3:3754

Abu Bakr narrated to us, he said: Muhammad ibn Fudayl narrated to us, from Husayn, from al-Haytham ibn Shihab, that he saw a man from his people praying while sitting cross-legged. He forbade him, but he refused to obey him. Al-Haytham said: I heard Abdullah ibn Mas’ud say: "That I should sit upon two heated stones is more beloved to me than that I should sit cross-legged in prayer."