Musannaf Ibn Abi Shaybah 6857 — Those who permitted that

Abu Bakr bin Abi Musa said: Sayyiduna Abu Musa (may Allah be pleased with him) came to Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) after Isha. Sayyiduna Umar bin al-Khattab said to him: "Why have you come?" He said: "I have come to talk with you." Sayyiduna Umar said: "At this hour?" Sayyiduna Abu Musa said: "It is a matter of religion." So Sayyiduna Umar sat with him, and the two of them talked for a long part of the night. Then Sayyiduna Abu Musa said: "O Commander of the Believers! The prayer (its time has come)." Sayyiduna Umar said: "We have been in prayer all along."