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. (Using translation from Ibn Mājah 461)
«أَنَّ رَسُولَ اللهِ ﷺ كَانَ إِذَا تَوَضَّأَ أَخَذَ كَفًّا مِنْ مَاءٍ فَنَضَحَ بِهِ فَرْجَهُ»