وَأَذَانٌ مِّنَ اللَّهِ وَرَسُولِهِ إِلَى النَّاسِ يَوْمَ الْحَجِّ الْأَكْبَرِ أَنَّ اللَّهَ بَرِيءٌ مِّنَ الْمُشْرِكِينَ ۙ وَرَسُولُهُ ۚ فَإِن تُبْتُمْ فَهُوَ خَيْرٌ لَّكُمْ ۖ وَإِن تَوَلَّيْتُمْ فَاعْلَمُوا أَنَّكُمْ غَيْرُ مُعْجِزِي اللَّهِ ۗ وَبَشِّرِ الَّذِينَ كَفَرُوا بِعَذَابٍ أَلِيمٍ
“And [it is] an announcement from Allah and His Messenger to the people on the day of the greater Hajj that Allah is disassociated from the disbelievers, and [so is] His Messenger. So if you repent, that is best for you; but if you turn away -- then know that you will not cause failure to Allah. And give tidings to those who disbelieve of a painful Punishment.”
This ayah is part of the opening of Surat al-Tawba, revealed -- as this event's own description states -- within hours of Abu Bakr RA's Hajj delegation departing Madinah, and proclaimed by Ali ibn Abi Talib RA during that Hajj.