Hadith
أَخْبَرَنَا الْحَسَنُ بْنُ مُحَمَّدٍ الزَّعْفَرَانِيُّ، قَالَ حَدَّثَنَا حَجَّاجُ بْنُ مُحَمَّدٍ، قَالَ ابْنُ جُرَيْجٍ أَخْبَرَنِي يَعْلَى، عَنْ سَعِيدِ بْنِ جُبَيْرٍ، عَنِ ابْنِ عَبَّاسٍ، أَنَّ نَاسًا، مِنْ أَهْلِ الشِّرْكِ أَتَوْا مُحَمَّدًا فَقَالُوا إِنَّ الَّذِي تَقُولُ وَتَدْعُو إِلَيْهِ لَحَسَنٌ لَوْ تُخْبِرُنَا أَنَّ لِمَا عَمِلْنَا كَفَّارَةً . فَنَزَلَتْ { وَالَّذِينَ لاَ يَدْعُونَ مَعَ اللَّهِ إِلَهًا آخَرَ } وَنَزَلَتْ { قُلْ يَا عِبَادِيَ الَّذِينَ أَسْرَفُوا عَلَى أَنْفُسِهِمْ } .
It was narrated from Ibn 'Abbas that :Some of the people of Shirk came to Muhammad [SAW] and said: "What you say and call people to is good, if only you could tell us that there is any expiation for what we have done." Then the Verses: "And those who invoke not any other ilah (god) along with Allah, or kill such a person as Allah has forbidden, except by right." And "Say: O 'Ibadi (My slaves) who have transgressed against themselves (by committing evil deeds and sins)" were revealed
Sahih · Abu Ghuddah
Sunan an-Nasa'i 4004 ·Book 37, Hadith 39·Also available on sunnah.com·