صحيح ابن خزيمه
Sahih Ibn Khuzaymah
جماع أبواب ذكر الماء الذي لا ينجس، والذي ينجس إذا خالطته نجاسةChapters on Water that is Pure and Impure
(93) بَابُ ذِكْرِ الدَّلِيلِ عَلَى أَنْ لَا تَوْقِيتَ فِي قَدْرِ الْمَاءِ الَّذِي يَتَوَضَّأُ بِهِ الْمَرْءُ، فَيَضِيقُ عَلَى الْمُتَوَضِّئِ أَنْ يَزِيدَ عَلَيْهِ أَوْ يَنْقُصَ مِنْهُ،Chapter 93: Evidence that there is no fixed amount of water for ablution, and it is not restricted
Hadith Q119
إِذْ لَوْ كَانَ لِقَدْرِ الْمَاءِ الَّذِي يَتَوَضَّأُ بِهِ الْمَرْءُ مِقْدَارٌ لَا يَجُوزُ أَنْ يَزِيدَ عَلَيْهِ وَلَا يَنْقُصَ مِنْهُ شَيْئًا، لَمَا جَازَ أَنْ يَجْتَمِعَ اثَنَانِ وَلَا جَمَاعَةٌ عَلَى إِنَاءٍ وَاحِدٍ، فَيَتَوَضَّئُوا مِنْهُ جَمِيعًا، وَالْعِلْمُ مُحِيطٌ أَنَّهُمْ إِذَا اجْتَمَعُوا عَلَى إِنَاءٍ وَاحِدٍ يَتَوَضَّئُونَ مِنْهُ؛ فَإِنَّ بَعْضَهُمْ أَكْثَرُ حَمْلًا لِلْمَاءِ مِنْ بَعْضٍ
Because if a specific amount of water had been prescribed for ablution, such that using less or more than that amount would not be permissible, then it would also be impermissible for two people or a group to perform ablution together from one vessel. This is because it is certain that when they perform ablution together from one vessel, some people will use more water and some will use less.
