Musannaf Ibn Abi Shayba 3:4058

Hushaym narrated to us, he said: Al-Mas'udi informed us, from Al-Qasim ibn Abd al-Rahman, that Ibn Mas'ud entered the mosque and saw people who had leaned their backs against the Qibla. He said: So Abdullah said to them, "Thus [you turn away] from the faces of the angels."