Sunan an-Nasa'i
It was narrated that 'Aishah said: "Tell your husbands to clean themselves with water, for I am too shy to tell them myself. The Messenger of Allah (ﷺ) used to do that."
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ قَتَادَةَ، عَنْ مُعَاذَةَ، عَنْ عَائِشَةَ، أَنَّهَا قَالَتْ مُرْنَ أَزْوَاجَكُنَّ أَنْ يَسْتَطِيبُوا بِالْمَاءِ فَإِنِّي أَسْتَحْيِيهِمْ مِنْهُ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يَفْعَلُهُ .
Grade: Sahih (Darussalam)
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