When Uthman placed his property at at-Ta'if and intended to settle there, he prayed four rak'ahs. The rulers after him followed the same practice.
Sunan Abi Dawud Book 11, Hadith 243
← Previous Hadith Uthman prayed four rak'ahs (at Mina) for he made it his home (for settlement).

Sunan Abi Dawud Book 11, Hadith 242 Next Hadith → Uthman offered complete prayer at Mina for the sake of bedouins who attended (hajj) in large numbers that year. He led the people four rak'ahs in prayer in order to teach them that the prayer (i.e. noon or afternoon prayer) essentially contained four rak'ahs.

Sunan Abi Dawud Book 11, Hadith 244