Musannaf Ibn Abi Shayba 3:2534

Abu Bakr narrated to us, he said: Safwan bin Isa narrated to us, from Al-Harith bin Abd al-Rahman, he said: I asked Sulayman bin Yasar about sleeping in the mosque. He said: How can you ask about this when the people of the Suffah used to sleep in it and pray in it?