The Quran

وَقالَ الَّذينَ كَفَروا لِلَّذينَ آمَنُوا اتَّبِعوا سَبيلَنا وَلنَحمِل خَطاياكُم وَما هُم بِحامِلينَ مِن خَطاياهُم مِن شَيءٍ ۖ إِنَّهُم لَكاذِبونَ

Muhammad Asad

And [He is aware, too, that] they who are bent on denying the truth speak [thus, as it were,] to those who have attained to faith: "Follow our way [of life], and we shall indeed take your sins upon ourselves!"¹But never could they take upon themselves² aught of the sins of those [whom they would thus mislead]:behold, they are liars indeed!

The above "saying" of the deniers of the truth is, of course, but a metonym for their attitude towards the believers; hence my interpolation, between brackets, of the words "as it were". The implication is that people who deny the validity of any spiritual commitment arising out of one's faith in "something that is beyond the reach of human perception" ~al-ghayb) - in this case, the existence of God - are, as a rule, unwilling to tolerate such a faith and such a commitment in others as well: and so they endeavour to bring the believers to their way of thinking by a sarcastic, contemptuous reference to the alleged irrelevance of the concept of "sin" as such.
Lit., "bear" - implying a reduction of the burden which the others would have to bear (Razi). See also next note.