Narrated Az-Zuhri: 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.
Explanation & Benefits
Shaykh Umar Farooq Saeedi
1964. Commentary: All four of these narrations are weak. Therefore, the only reason for Uthman (radi Allahu anhu) performing the full prayer at Mina is the permissibility for a traveler to perform the full prayer instead of shortening it (qasr). There is no other reason besides this.
Source: Sunan Abu Dawood – Commentary by Shaykh Umar Farooq Saeedi, Page: 1964