Uthman used to bathe once every day from the time he became Muslim. One day I prepared water for his ablution before the prayer. After he performed the ablution, he said, "I had intended to tell you a hadith I heard from the Messenger of Allah ﷺ." Then he said, "It now seems best to me not to tell it to you."Hakam bin Abu al-As said, "Commander of the Believers, if it is something good, we will take it up, and if it is something bad, we will guard against it."Uthman replied, "Then I will tell it to you. The Messenger of Allah ﷺ performed an ablution like this one, then he said, 'Whoever performs an ablution like this and does it well, then rises to prayer and completes its bowing and prostration properly, will have whatever lies between it and the next prayer expiated for him, so long as he does not commit a grave sin,' meaning a major sin."
حدثنا عفان حدثنا أبو عوانة عن عاصم عن المسيب عن موسى بن طلحة
كان عثمان رضي الله عنه يغتسل كل يوم مرة من منذ أسلم فوضعت وضوءا له ذات يوم للصلاة فلما توضأ قال إني أردت أن أحدثكم بحديث سمعته من رسول الله ﷺ ثم قال بدا لي أن لا أحدثكموه فقال الحكم بن أبي العاص يا أمير المؤمنين إن كان خيرا فنأخذ به أو شرا فنتقيه قال فقال فإني محدثكم به توضأ رسول الله ﷺ هذا الوضوء ثم قال من توضأ هذا الوضوء فأحسن الوضوء ثم قام إلى الصلاة فأتم ركوعها وسجودها كفرت عنه ما بينها وبين الصلاة الأخرى ما لم يصب مقتلة يعني كبيرة
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Its isnad is sahih. Aasim is Ibn Bahdala, who is Ibn Abu Najud, with the noon vowelized as fatha, the Asadi. Musayab is Ibn Rafi al-Asadi al-Kahili. Musa bin Talha bin Ubaydullah al-Qurashi al-Taymi is one of the senior Tabiin, who narrates from Uthman and Ali and others, but here he narrated from Humran, from Uthman.