Silsilat al-Ahadith al-Sahihah

It is narrated from Sayyiduna Suraqah bin Malik bin Ju'sham (may Allah be pleased with him) that when he came to the Messenger of Allah (peace and blessings be upon him), he conveyed some matters to his people and taught them (the matters of religion). One day, a man jokingly said to him: "For Suraqah, only this remains, that he should teach you the manner of relieving yourselves." Suraqah (turning the matter to seriousness) said: "When you go to relieve yourselves, avoid sitting in shaded places and on pathways, arrange for small stones, put pressure on your (left) shin, and perform istinja (cleansing) with an odd number (of stones)."