Amr bin Shu'ayb narrates from his grandfather (may Allah be pleased with him) that a Bedouin came to the Prophet (peace and blessings be upon him) and asked him about ablution. He (peace and blessings be upon him) showed him, washing each part three times, then he (peace and blessings be upon him) said: "This is (the method of) ablution. Whoever does more than this has done wrong, or has transgressed and done injustice."
(b) It is narrated from Imam al-Thawri in a connected (mawsul) form. [Hasan. Recorded by al-Tabarani in al-Kabir: 174]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 373