Sahih Muslim 43
Sahih Muslim · Book 1: The Book of Faith · Clarification of those characteristics which, if a person attains them, he will find the sweetness of faith
A similar hadith has been reported on the authority of Anas (with another chain of transmitters) with the exception of these words:
حَدَّثَنَا إِسْحَاقُ بْنُ مَنْصُورٍ ، أَنْبَأَنَا النَّضْرُ بْنُ شُمَيْلٍ ، أَنْبَأَنَا حَمَّادٌ ، عَنْ ثَابِتٍ ، عَنْ أَنَسٍ ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم بِنَحْوِ حَدِيثِهِمْ غَيْرَ أَنَّهُ قَالَ " مِنْ أَنْ يَرْجِعَ يَهُودِيًّا أَوْ نَصْرَانِيًّا " .
that he again becomes a Jew or a Christian.