It is narrated from Sayyidah Aishah (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) urinated, and Sayyiduna Umar (may Allah be pleased with him) came with a cup of water. He (peace and blessings be upon him) said: "O Umar, what is this?" Sayyiduna Umar (may Allah be pleased with him) said: You may perform ablution with it. He (peace and blessings be upon him) said: "I have not been commanded to perform ablution every time I urinate, and if I were to do so, it would become a Sunnah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 551
Isa bin Yazdad narrates from his father (may Allah be pleased with him) that when the Prophet (peace and blessings be upon him) urinated, he would clean his private part three times.
(b) Abdullah bin Adi says that Isa bin Yazdad narrates from his father in mursal form, and it is not authentic. Al-Bukhari said: Isa bin Yazdad is known only through this narration.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 552