Narrated Abu Hurairah: The Messenger of Allah ﷺ said: The prayer of a person who does not perform ablution is not valid, and the ablution of a person who does not mention the name of Allah (in the beginning) is not valid.
Hadith Referenceسنن ابي داود / كتاب الطهارة / 101
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:حسن, مشكوة المصابيح (403), وللحديث شواهد منها ما أخرجه ابن ماجه (397) وسنده حسن