﴿ وَلَقَدْ فَتَنَّا ٱلَّذِينَ مِن قَبْلِهِمْ ۖ فَلَيَعْلَمَنَّ ٱللَّهُ ٱلَّذِينَ صَدَقُوا۟ وَلَيَعْلَمَنَّ ٱلْكَٰذِبِينَ ﴾

“Yea, indeed, We did test those who lived before them; and so, [too, shall be tested the people now living: and] most certainly will God mark out those who prove themselves true, and most certainly will He mark out those who are lying.”

(Lo! We tested those who were before you) before the Companions of Muhammad (pbuh) after the demise of their prophets, with caprice, blameworthy innovations and the violation of sanctities. (Thus Allah knoweth) in order that Allah sees and distinguishes (those who are sincere) in their faith by avoiding caprice, blameworthy innovation and by shunning that which is unlawful, (and knoweth those who feign) i.e. the insincere in their faith who follow caprice, blameworthy innovation and the violation of sanctities.