It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that Sayyiduna Umar bin Khattab (may Allah be pleased with him) delivered a sermon at the place of Jabiyah, and he said that the Messenger of Allah (peace and blessings be upon him) stood among us and he said... and he also mentioned this matter... and he narrated this hadith.
Hadith Referenceمسند الشهاب / 403
Hadith Gradingمحدثین:إسناده صحيح
Hadith Takhrij«إسناده صحيح ، وأخرجه الترمذي : 2165، والسنن الكبرى للنسائى : 9181»
Brief Explanation
Explanation: The person who feels happiness upon doing a good deed and feels sorrow upon committing a bad deed, then he is a believer (mumin); that is, this is evidence of his being a believer. Because disbelievers (kuffar) and hypocrites (munafiqun) neither rejoice at good deeds nor feel regret over sins; to them, good and evil are the same. However, Allah Ta'ala says:
﴿وَلَاتَسْتَوِيالْحَسَنَةُوَلَاالسَّيِّئَةُ﴾ (Ha Mim As-Sajdah: 34) "Good and evil are not equal."
Disbelievers and hypocrites have no concern for the future; that is why they consider this world to be everything and remain engrossed in it. Their hearts have died, and their inner feelings have vanished. Whereas, a believer has a future before him—a future that has no end. Therefore, he considers this world to be temporary and remains concerned about his future, that is, the Hereafter (akhirah). This is the reason that, upon doing a good deed, he naturally feels happiness, his heart is content, and if he commits a bad deed, his nature becomes disturbed, and he does not find peace until he performs some good deed that removes that bad deed.