Musannaf Ibn Abi Shayba 3:5880

Abu Bakr narrated to us, he said: Hatim ibn Isma'il narrated to us, from 'Abd al-Rahman ibn Harmala, that a man came to Sa'id ibn al-Musayyib and said: "I am a shepherd of camels; I milk them until, when evening comes, I pray Maghrib, then I lie down and sleep through 'Isha'." He said: "Do not sleep until you pray it. But if you fear that you will sleep, then combine between them."