Musannaf Ibn Abi Shaybah 3263 — All the prayer times

Ali bin Amr said: A letter from Sayyiduna Umar (may Allah be pleased with him) came to us, in which was written: "Pray Fajr while the stars are shining and visible. Pray Zuhr when the sun has declined from the middle of the sky. Pray Asr while the sun is white and bright. Pray Maghrib when the sun sets." And he gave latitude regarding the Isha prayer.