Sunan Abi Dawud 822
سنن أبي داود#822SahihUbadah b. al-Samit reported the Messenger of Allah (ﷺ) as saying :the prayer is not valid I one does not recite fatihat al-kitab and something more, sufyan( the narrator) said: This applies to a man who prays alone
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Muhyi Al-Din Abdul HamidSahih
Shuaib Al ArnautSahih
Zubair Ali ZaiSahih Muslim (394)
In-book reference: 2:432