Hadith: He who does good in Islam will not be punished for what he did during jāhiliyyah, and he who commits evil in Islam will be punished for the previous and later deeds

عَنِ ابْنِ مَسْعُودٍ رَضِيَ اللَّهُ عَنْهُ، قَالَ:
قَالَ رَجُلٌ: يَا رَسُولَ اللهِ، أَنُؤَاخَذُ بِمَا عَمِلْنَا فِي الْجَاهِلِيَّةِ؟ قَالَ: «مَنْ أَحْسَنَ فِي الْإِسْلَامِ لَمْ يُؤَاخَذْ بِمَا عَمِلَ فِي الْجَاهِلِيَّةِ، وَمَنْ أَسَاءَ فِي الْإِسْلَامِ أُخِذَ بِالْأَوَّلِ وَالْآخِرِ».
[صحيح] - [متفق عليه] - [صحيح البخاري: 6921]

Ibn Mas‘ūd (may Allah be pleased with him) reported:
A man said: "O Messenger of Allah, will we be punished for what we did during jāhiliyyah (the pre-Islamic period of ignorance)?" He said: "He who does good in Islam will not be punished for what he did during jāhiliyyah, and he who commits evil in Islam will be punished for the previous and later deeds."
[Authentic hadith] - [Narrated by Bukhari & Muslim] - [Sahih Bukhari - 6921]

Explanation

The Prophet (may Allah's peace and blessings be upon him) points out the merit of entering Islam. He who embraces Islam and becomes a committed, sincere, and truthful Muslim will not be punished for the sins he committed during jāhiliyyah. In contrast, he who does wrong after entering Islam, by being a hypocrite or renouncing Islam, will be punished for what he did both during his period of disbelief and after entering Islam.