Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) says: I prayed two rak'ahs at Mina with the Prophet (peace and blessings be upon him), and two rak'ahs with Sayyiduna Abu Bakr (may Allah be pleased with him) and Sayyiduna Umar (may Allah be pleased with him) as well, and likewise with Sayyiduna Uthman (may Allah be pleased with him) at the beginning of his caliphate; then he used to pray four rak'ahs.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5327