It is narrated from Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "The ablution of that person is not valid who does not recite «بِسْمِاللّٰہِ» over it."
Hadith Takhrij«قال الالباني: حسن ۔ أخرجه ابن ماجه: 397، (انظر مسند أحمد ترقيم الرسالة: 11371 ترقیم بيت الأفكار الدولية: 11391»
Brief Explanation
Benefits: … Ibn Humam Hanafi has declared this hadith to be hasan and, on this basis, has deemed reciting “Bismillah” at the beginning of ablution (wudu) to be obligatory. (Sharh Fath al-Qadir: 1/23) And Ibn Nujaym Hanafi has also called it hasan. (al-Bahr al-Ra’iq: 1/18)