Sahih Bukhari – Hadith No : 5028

Narrated Zirr bin Hubaish: I asked Ubai bin Ka`b regarding the two Muwwidhat (Surats of taking refuge with Allah). He said, “I asked the Prophet about them, He said, ‘These two Surats have been recited to me and I have recited them (and are present in the Qur’an).’ So, we say as Allah’s Apostle said (i.e., they are part of the Qur’an.”

Hadith In Arabic Text :

حدثنا قتيبة بن سعيد، حدثنا سفيان، عن عاصم، وعبدة، عن زر بن حبيش، قال سألت أبى بن كعب عن المعوذتين، فقال سألت رسول الله صلى الله عليه وسلم فقال قيل لي فقلت فنحن نقول كما قال رسول الله صلى الله عليه وسلم‏.‏

Chapter : Prophetic Commentary on the Qur’an (Tafseer of the Prophet (pbuh)) – كتاب التفسير