Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says: Sleep was mentioned before the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) said: "Sleep! And when you wake up, use the miswak!"
This narration was recorded by Imam al-Bazzar; its chain contains a narrator, Yahya bin al-Mundhir, whom Imam al-Daraqutni (may Allah have mercy on him) and others declared da'if (weak).