Majma al-Zawaid — Hadith 1004

It is reported about Sayyiduna Suraqah bin Malik bin Ju'shum (may Allah be pleased with him) that when he came back (to his own area) from the Prophet (peace and blessings be upon him), he would tell his people what he had learned and teach them (the rulings of the Shari'ah). One day a man said, mocking him: All that is left for Suraqah now is to teach you how to relieve yourselves! Sayyiduna Suraqah (may Allah be pleased with him) said: When you go to relieve yourselves, avoid sitting in the shade or on the roads; take small stones, rest your weight upon your legs, use stones to cleanse yourselves, and use an odd number.
Al-Tabarani recorded it in al-Mu'jam al-Awsat, and its chain is hasan (good).