Qur'an 18:2

قَيِّمًا لِّيُنذِرَ بَأْسًا شَدِيدًا مِّن لَّدُنْهُ وَيُبَشِّرَ ٱلْمُؤْمِنِينَ ٱلَّذِينَ يَعْمَلُونَ ٱلصَّـٰلِحَـٰتِ أَنَّ لَهُمْ أَجْرًا حَسَنًا

(But hath made it) straight, to give warning of stern punishment from Him, and to bring unto the believers who do good works the news that theirs will be a fair reward,