Surah Al-Nahl (The Bees), Verse 91

وَاَوْفُوْا بِعَهْدِ اللّٰهِ اِذَا عٰهَدْتُّمْ وَلَا تَنْقُضُوا الْاَیْمَانَ بَعْدَ تَوْكِیْدِهَا وَقَدْ جَعَلْتُمُ اللّٰهَ عَلَیْكُمْ كَفِیْلًا اِنَّ اللّٰهَ یَعْلَمُ مَا تَفْعَلُوْنَ ۟

Wa awfoo bi Ahdil laahi izaa 'aahattum wa laa tanqudul aimaana ba'da tawkeedihaa wa qad ja'altumul laaha 'alaikum kafeelaa; innal laaha ya'lamu maa taf'aloon

“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 (Yusuf Ali Translation)