A man said, "O Allah's Messenger (ﷺ)! Shall we be punished for what we did in the Prelslamic Period of ignorance?" The Prophet (ﷺ) said, "Whoever does good in Islam will not be punished for what he did in the Pre-lslamic Period of ignorance and whoever does evil in Islam will be punished for his former and later (bad deeds).
Sahih al-Bukhari Book 88, Hadith 4
← Previous Hadith A bedouin came to the Prophet (ﷺ) and said, "O Allah's Messenger (ﷺ)! What are the biggest sins?: The Prophet (ﷺ) said, "To join others in worship with Allah." The bedouin said, "What is next?" The Prophet (ﷺ) said, "To be undutiful to one's parents." The bedouin said "What is next?" The Prophet (ﷺ) said "To take an oath 'Al-Ghamus." The bedouin said, "What is an oath 'Al-Ghamus'?" The Prophet (ﷺ) said, "The false oath through which one deprives a Muslim of his property (unjustly).

Sahih al-Bukhari Book 88, Hadith 3 Next Hadith → Some Zanadiqa (atheists) were brought to `Ali and he burnt them. The news of this event, reached Ibn `Abbas who said, "If I had been in his place, I would not have burnt them, as Allah's Messenger (ﷺ) forbade it, saying, 'Do not punish anybody with Allah's punishment (fire).' I would have killed them according to the statement of Allah's Messenger (ﷺ), 'Whoever changed his Islamic religion, then kill him.'"

Sahih al-Bukhari Book 88, Hadith 5