Musannaf Ibn Abi Shaybah 14523 — The prayer at Mina: how many rak'ahs

It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) prayed two rak'ahs at Mina. Then after him (peace and blessings be upon him) Abu Bakr al-Siddiq prayed two rak'ahs, then after Abu Bakr al-Siddiq Umar prayed two rak'ahs, and Uthman prayed two rak'ahs in the early years of his caliphate. Then Uthman began praying four rak'ahs. When Ibn Umar (may Allah be pleased with them both) prayed with the imam he prayed four rak'ahs, and when he prayed alone he prayed two rak'ahs.