Sunan Ibn Majah 510
سنن ابن ماجه#510SahihSulaiman bin Buraidah narrated from his father that:The Prophet used to perform ablution for every prayer, but on the day of the conquest of Makkah, he performed all of the prayers with one ablution
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Fouad Abd al-BaqiSahih
Shuaib Al ArnautSahih
Zubair Ali ZaiSahih Muslim
In-book reference: 1:244