Musannaf Ibn Abi Shaybah

It is narrated from Hazrat Abu Saeed Khudri (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him) said: "The one who does not mention the name of Allah before performing ablution, his ablution is not valid."

It is narrated from Hazrat Abu Sufyan bin Huwaiteb that I heard the Messenger of Allah, peace and blessings be upon him, saying: The prayer of one who does not perform ablution is not valid, and the ablution of one who does not mention the name of Allah before it is not valid.

Hazrat Umrah says that I asked Hazrat Aisha (may Allah be pleased with her) about the manner of the Prophet Muhammad’s (peace and blessings be upon him) prayer, so she replied, "When the Prophet Muhammad (peace and blessings be upon him) would begin to perform ablution, he would first place his hand in the water and recite «بسم الله», then perform ablution and complete it thoroughly and in an excellent manner."

Hazrat Abu Bakr (may Allah be pleased with him) says that when a person recites «بسم الله» while performing ablution, his entire body becomes purified, and if he does not recite «بسم الله», then only that part becomes purified where the water of ablution reaches.

Hasan Basri says that a person should recite Bismillah before performing ablution; if he does not recite Bismillah, his ablution will still be valid.