﴿ إِنَّمَا ٱلْمُؤْمِنُونَ ٱلَّذِينَ ءَامَنُوا۟ بِٱللَّهِ وَرَسُولِهِۦ ثُمَّ لَمْ يَرْتَابُوا۟ وَجَٰهَدُوا۟ بِأَمْوَٰلِهِمْ وَأَنفُسِهِمْ فِى سَبِيلِ ٱللَّهِ ۚ أُو۟لَٰٓئِكَ هُمُ ٱلصَّٰدِقُونَ ﴾

“[Know that true] believers are only those who have attained to faith in God and His Apostle and have left all doubt behind, and who strive hard in God’s cause with their possessions and their lives: it is they, they who are true to their word!”

Allah then explained the traits of those who are true in their faith, saying: (The (true) believers) who are sincere in their faith (are those only who believe in Allah and His messenger and afterward doubt not) in their faith, (but strive with their wealth and their lives for the cause of Allah) in obedience to Allah. (Such are the sincere) who are true in their faith and striving.