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
(85) بَابُ الدَّلِيلِ عَلَى أَنَّ سُؤْرَ الْحَائِضِ لَيْسَ بِنَجَسٍ،Chapter 85: Evidence that the leftover water of a menstruating woman is not impure
Hadith Q110
وَإِبَاحَةِ الْوُضُوءِ وَالْغُسْلِ بِهِ، إِذْ هُوَ طَاهِرٌ غَيْرُ نَجِسٍ، إِذْ لَوْ كَانَ سُؤْرُ حَائِضٍ نَجِسًا لَمَا شَرِبَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ مَاءً نَجِسًا غَيْرَ مُضْطَرٍّ إِلَى شُرْبِهِ
And performing ablution and ghusl with it is permissible because it is pure, not impure, because if the leftover water of a menstruating woman was impure, then the Prophet (peace be upon him) would not have drunk the impure water, especially when he (peace be upon him) was not even compelled to drink it.
