📖 Abu Umamah RadhiAllahu 'anhu narrated: A man asked the Prophet SallAllahu 'alaihi wa sallam, “What is faith?” The Messenger of Allah SallAllahu 'alaihi wa sallam said: "If you are happy with your good deeds and saddened by your evil deeds, then you are a believer."
The man said, “O Messenger of Allah, what is sin?” The Prophet SallAllahu 'alaihi wa sallam said: "If something wavers in your soul (makes you feel restless), then you should abandon it."
Source: Musnad Aḥmad 21695, Grade: Sahih
📖 Abdur Rahman ibn Mu’awiyah RadhiAllahu 'anhu narrated: A man asked the Messenger of Allah SallAllahu 'alaihi wa sallam saying, “O Messenger of Allah, what is lawful and unlawful for me?” The Prophet SallAllahu 'alaihi wa sallam struck his chest and he said, "Whatever your heart rejects, abandon it."
Source: Al-Zuhd wal-Raqā’iq 1147
Grade: Sahih (Authentic) according to Al-Albani
📖 Abu Tha’laba RadhiAllahu 'anhu narrated: I said, “O Messenger of Allah, tell me what is lawful and unlawful for me.” The Prophet SallAllahu 'alaihi wa sallam said, "Righteousness is serenity in the soul and tranquility in the heart. Sin is not serene in the soul and not satisfying to the heart, even if the judge gives you approval."
Source: Musnad Aḥmed 17396
Grade: Sahih (Authentic) according to Al-Albani