Sahih al-Bukhari 188
Sahih al-Bukhari · Book 4: Ablutions (Wudu') · The using of the remaining water after ablution
Abu Musa said:
وَقَالَ أَبُو مُوسَى دَعَا النَّبِيُّ صلى الله عليه وسلم بِقَدَحٍ فِيهِ مَاءٌ، فَغَسَلَ يَدَيْهِ وَوَجْهَهُ فِيهِ، وَمَجَّ فِيهِ ثُمَّ قَالَ لَهُمَا اشْرَبَا مِنْهُ، وَأَفْرِغَا عَلَى وُجُوهِكُمَا وَنُحُورِكُمَا.
The Prophet asked for a tumbler containing water and washed both his hands and face in it and then threw a mouthful of water in the tumbler and said to both of us (Abu Musa and Bilal), "Drink from the tumbler and pour some of its water on your faces and chests."