وَأَوْفُوا بِعَهْدِ اللَّهِ إِذَا عَاهَدْتُمْ وَلَا تَنْقُضُوا الْأَيْمَانَ بَعْدَ تَوْكِيدِهَا وَقَدْ جَعَلْتُمُ اللَّهَ عَلَيْكُمْ كَفِيلًا ۚ إِنَّ اللَّهَ يَعْلَمُ مَا تَفْعَلُونَ
Fulfil the Covenant of Allah when ye have entered into it, and break not your oaths after ye have confirmed them; indeed ye have made Allah your surety; for Allah knoweth all that ye do. Quran 16: 91

يَا أَيُّهَا الَّذِينَ آمَنُوا كُتِبَ عَلَيْكُمُ الصِّيَامُ كَمَا كُتِبَ عَلَى الَّذِينَ مِنْ قَبْلِكُمْ لَعَلَّكُمْ تَتَّقُونَ
O ye who believe! Fasting is prescribed to you as it was prescribed to those before you, that ye may (learn) self-restraint. Q 2: 183