(48) باب التَّسْمِيَةِ عَلَى الْوُضُوءِ
Narrated AbuHurayrah:
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.
Reference: Sunan Abi Dawud 101
In-book reference: Book 1, Hadith 101
English translation: Book 1, Hadith 101