Uthman bin Affan performed the prayer in full at Mina because of the bedouins, who had come in large numbers that year. He led the people in four units of prayer to teach them that the prayer is four.
حدثنا موسى بن إسمعيل حدثنا حماد عن أيوب
أن عثمان بن عفان أتم الصلاة بمنى من أجل الأعراب لأنهم كثروا عامئذ فصلى بالناس أربعا ليعلمهم أن الصلاة أربع
No references are available.
[Its chain is daif] Bayhaqi reported it, 3/144, from the hadith of Abu Dawud, through this chain, and the chain is disconnected as mentioned before, h: 1961.