Evidence that the one who is content with Allah as his Lord, Islam as his religion and Muhammad (saws) as his prophet, then he is a believer, even if he commits major sins Sahih Muslim 34
Arabic hadith text
حَدَّثَنَا مُحَمَّدُ بْنُ يَحْيَى بْنِ أَبِي عُمَرَ الْمَكِّيُّ، وَبِشْرُ بْنُ الْحَكَمِ، قَالاَ حَدَّثَنَا عَبْدُ الْعَزِيزِ، - وَهُوَ ابْنُ مُحَمَّدٍ - الدَّرَاوَرْدِيُّ عَنْ يَزِيدَ بْنِ الْهَادِ، عَنْ مُحَمَّدِ بْنِ إِبْرَاهِيمَ، عَنْ عَامِرِ بْنِ سَعْدٍ، عَنِ الْعَبَّاسِ بْنِ عَبْدِ الْمُطَّلِبِ، أَنَّهُ سَمِعَ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ "ذَاقَ طَعْمَ الإِيمَانِ مَنْ رَضِيَ بِاللَّهِ رَبًّا وَبِالإِسْلاَمِ دِينًا وَبِمُحَمَّدٍ رَسُولاً "
Translation
It is narrated on the authority of 'Abbas b. 'Abdul-Muttalib that he heard the Messenger of Allah saying
He has found the taste of faith (iman) who is content with Allah as his Lord, with Islam as his religion (code of life) and with Muhammad (ﷺ) as his Prophet.