From Sahih Bukhari (Hadith 7269):
Narrated Anas bin Malik:That he heard `Umar speaking while standing on the pulpit of the Prophet (ﷺ) in the morning (following the death of the Prophet), when the people had sworn allegiance to Abu Bakr. He said the Tashah-hud before Abu Bakr, and said, "Amma Ba'du (then after) Allah has chosen for his Apostle what is with Him (Paradise) rather than what is with you (the world). This is that Book (Qur'an) with which Allah guided your Apostle, so stick to it, for then you will be guided on the right path as Allah guided His Apostle with it
Reference: Bukhari 7269