كتاب الطهارة
2  
The Book of Purification
(31)
Chapter: The ruling on the urine of a nursing infant and how to wash it
(31)
باب حُكْمِ بَوْلِ الطِّفْلِ الرَّضِيعِ وَكَيْفِيَّةِ غَسْلِهِ ‏‏
Sahih Muslim 287a

Umm Qais daughter of Mihsan reported that she came to the Messenger of Allah (ﷺ) with her child. who was not yet weaned, and she placed him in his lap; and he urinated in his (Holy Prophet's) lap. He (the Holy Prophet) did nothing more than spraying water over it.

حَدَّثَنَا مُحَمَّدُ بْنُ رُمْحِ بْنِ الْمُهَاجِرِ، أَخْبَرَنَا اللَّيْثُ، عَنِ ابْنِ شِهَابٍ، عَنْ عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ، عَنْ أُمِّ قَيْسٍ بِنْتِ مِحْصَنٍ، أَنَّهَا أَتَتْ رَسُولَ اللَّهِ صلى الله عليه وسلم بِابْنٍ لَهَا لَمْ يَأْكُلِ الطَّعَامَ فَوَضَعَتْهُ فِي حِجْرِهِ فَبَالَ - قَالَ - فَلَمْ يَزِدْ عَلَى أَنْ نَضَحَ بِالْمَاءِ ‏.‏
Reference : Sahih Muslim 287a
In-book reference : Book 2, Hadith 131
USC-MSA web (English) reference : Book 2, Hadith 563
  (deprecated numbering scheme)