The Prophet (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 Referenceصحیح الجامع الصغیر / حرف الميم / 5551
Hadith Gradingالألبانی:حسن
Hadith Takhrij[حم د هـ] عن عائشة. المشكاة ٣٦٨، صحيح أبي داود ٣٢.