He saw the Messenger of Allah perform ablution then take a handful of water and sprinkle it over his private area to remove any doubts about urine drippings.
أَنَّهُ رَأَى رَسُولَ اللَّهِ ﷺ تَوَضَّأَ ثُمَّ أَخَذَ كَفًّا مِنْ مَاءٍ فَنَضَحَ بِهِ فَرْجَهُ