(a) Muhammad bin Abd al-Rahman bin Thawban (may Allah have mercy on him) said that the Messenger of Allah (peace and blessings be upon him) said: "When anyone's hand touches his private part, let him perform ablution."
(b) In another narration, Sayyiduna Jabir (may Allah be pleased with him) narrates it from the Prophet (peace and blessings be upon him).
(c) Imam al-Shafi'i (may Allah have mercy on him) said: I heard many of the huffaz (hadith masters) narrate it, but they did not mention Sayyiduna Jabir (may Allah be pleased with him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 644