"The Messenger of Allah ﷺ said: 'When any one of you gets up after (sleeping) at night, let him not put his hand into the vessel until he has poured water on it two or three times, for none of you knows where his hand spent the night.'" (Using translation from Nasāʾī 441)
قَالَ رَسُولُ اللهِ ﷺ إِذَا قَامَ أَحَدُكُمْ مَنَ اللَّيْلِ فَلَا يُدْخِلْ يَدَهُ فِي الْإِنَاءِ حَتَّى يُفْرِغَ عَلَيْهَا مَرَّتَيْنِ أَوْ ثَلَاثًا فَإِنَّهُ لَا يَدْرِي أَيْنَ بَاتَتْ يَدُهُ وَكَذَلِكَ قَالَهُ ابْنُ هُرْمُزَ عَنْ أَبِي هُرَيْرَةَ