Sahih Bukhari Volume 6, Book 60, Hadith Number 501.

Narrated By Zirr bin Hubaish : I asked Ubai bin Ka’b, “O Abu AlMundhir! Your brother, Ibn Mas’ud said so-and-so (i.e., the two Mu’awwidh-at do not belong to the Quran).” Ubai said, “I asked Allah’s Apostle about them, and he said, ‘They have been revealed to me, and I have recited them (as a part of the Quran),” So Ubai added, “So we say as Allah’s Apostle has said.”