The father of a man from Banu Mudlij said: Sayyiduna Suraqah bin Malik bin Ju'shum (may Allah be pleased with him) came from the Messenger of Allah (peace and blessings be upon him) and said: "The Messenger of Allah (peace and blessings be upon him) taught us such-and-such." At that, a man said mockingly: "Did he also teach you how to relieve yourselves?" Sayyiduna Suraqah (may Allah be pleased with him) said: "Yes, by the One who sent him (peace and blessings be upon him) with the truth! He (peace and blessings be upon him) commanded us to lean on the left (foot) and keep the right (foot) raised."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6575