Narrated 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 Qur'an)." Ubai said, "I asked Allah's Messenger (ﷺ) about them, and he said, 'They have been revealed to me, and I have recited them (as a part of the Qur'an)," So Ubai added, "So we say as Allah's Messenger (ﷺ) has said."

حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا سُفْيَانُ، حَدَّثَنَا عَبْدَةُ بْنُ أَبِي لُبَابَةَ، عَنْ زِرِّ بْنِ حُبَيْشٍ، وَحَدَّثَنَا عَاصِمٌ، عَنْ زِرٍّ، قَالَ سَأَلْتُ أُبَىَّ بْنَ كَعْبٍ قُلْتُ يَا أَبَا الْمُنْذِرِ إِنَّ أَخَاكَ ابْنَ مَسْعُودٍ يَقُولُ كَذَا وَكَذَا‏.‏ فَقَالَ أُبَىٌّ سَأَلْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم فَقَالَ لِي قِيلَ لِي‏.‏ فَقُلْتُ، قَالَ فَنَحْنُ نَقُولُ كَمَا قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم‏.‏
USC-MSA web (English) reference : Vol. 6, Book 60, Hadith 501
Arabic reference : Book 65, Hadith 4977