Sunan an-Nasa'i, Hadith 5676 ⓘ
It was narrated that Sa'eed bin Al-Musayyab said: "'Umar, may Allah be pleased with him, banished Rabi'ah bin Umaiyah to Khaibar for drinking Khamr, and he went and joined Heraclius and became a Christian. 'Umar, may Allah be pleased with him, said: 'I will never expel any Muslim after this.'"
أَخْبَرَنَا زَكَرِيَّا بْنُ يَحْيَى، قَالَ حَدَّثَنَا عَبْدُ الأَعْلَى بْنُ حَمَّادٍ، قَالَ حَدَّثَنَا مُعْتَمِرُ بْنُ سُلَيْمَانَ، قَالَ حَدَّثَنِي عَبْدُ الرَّزَّاقِ، عَنْ مَعْمَرٍ، عَنِ الزُّهْرِيِّ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، قَالَ غَرَّبَ عُمَرُ رضى الله عنه رَبِيعَةَ بْنَ أُمَيَّةَ فِي الْخَمْرِ إِلَى خَيْبَرَ فَلَحِقَ بِهِرَقْلَ فَتَنَصَّرَ فَقَالَ عُمَرُ رَضِيَ اللَّهُ عَنْهُ لاَ أُغَرِّبُ بَعْدَهُ مُسْلِمًا .
also referenced under: Book 51, Hadith 138 (In-Book) & Volume 6, Book 51, Hadith 5679 (DarusSalam)