The Messenger of Allah ﷺ said, "When one of you cleans himself with stones, let him use an odd number."
قال رسول الله ﷺ: إذا استجمر أحدكم فليوتر.
No references are available.
Muslim narrated it in the Book of Purification (239), through the route of Abdul-Razzaq, who said, Ibn Jurayj narrated to us, Abu Zubayr informed me, that he heard Jabir bin Abdullah say, and then he mentioned the hadith.