It is narrated from Sayyiduna Thawban (may Allah be pleased with him), the freed slave of the Messenger of Allah (peace and blessings be upon him), that the Messenger of Allah (peace and blessings be upon him) said: "Whoever calls for water for ablution, and then, at the moment he finishes his ablution, says: 'Ashhadu an la ilaha illallah, wa ashhadu anna Muhammadan rasulullah, Allahumma-j'alni mina-t-tawwabin, wa-j'alni mina-l-mutatahhirin' (I bear witness that there is no deity worthy of worship except Allah, and I bear witness that Muhammad (peace and blessings be upon him) is the Messenger of Allah. O Allah, make me among those who repent often and make me among those who purify themselves), the eight gates of Paradise are opened for him, so that he may enter by whichever of them he wishes."
No one narrated this hadith from al-A'mash (may Allah have mercy on him) except Miswar bin Muwarri' (may Allah have mercy on him).
Hadith Referenceالمعجم الأوسط / باب العين / 4895
Hadith Gradingمحدثین:غريب، تفرد به مسور بن مورع ولم يعرفه الهيثمي
Hadith Takhrij«قال الهيثمي: قال في الأوسط تفرد به مسور بن مورع ولم أجد من ترجمه وفيه أحمد بن سهيل الوراق ذكره ابن حبان في الثقات وفي إسناد الكبير أبو سعيد البقال والأكثر على تضعيفه ووثقه بعضهم «مجمع الزوائد ومنبع الفوائد، ج 1، ص 239»» «أخرجه الطبراني فى «الكبير» برقم: 1441»