Sayyidah Umm Qays bint Mihsan (may Allah be pleased with her) said: I came to the Prophet (peace and blessings be upon him) with my suckling son. The Prophet (peace and blessings be upon him) seated the child in his lap, and he urinated on him (peace and blessings be upon him). He (peace and blessings be upon him) called for water and sprinkled it over it, but did not wash it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4151