Jabir bin 'Abdullah reported that he heard the Messenger of Allah (ﷺ) say: When anyone wipes himself with pebbles (after answering the call of nature) he should do this odd number of times.
Explanation & Benefits
Shaykh Maulana Abdul Aziz Alvi
Hadith Commentary:
Benefits and Issues:
All of the aforementioned narrations establish that in istinja (purification after relieving oneself), one should use an odd number of stones (three, five, or seven). The use of three is obligatory, and using more than three depends on necessity. Observing odd numbers beyond three is better and more virtuous, but it is not obligatory.
Source: Tuhfat al-Muslim: Commentary on Sahih Muslim, Page: 565