Musannaf Ibn Abi Shayba 3:5392

Ya'la ibn 'Ubayd narrated to us, from Abu Sinan, from al-'Ala' ibn Badr, from Abu al-Sha'tha' al-Muharibi, from Salman, who said: "When you have prayed the morning prayer, remember Allah until the sun rises. If you do not do so, then sleep, for the sleeper is safe."