Sayyidah Busrah bint Safwan (may Allah be pleased with her) said: The things that require ablution were mentioned in the presence of the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) said: "And whoever touches the penis, let him perform ablution."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20869