Quran 16:94 from Surah An-Nahl on Divine Marvels.
وَلَا تَتَّخِذُوٓاْ أَيۡمَٰنَكُمۡ دَخَلَۢا بَيۡنَكُمۡ فَتَزِلَّ قَدَمُۢ بَعۡدَ ثُبُوتِهَا وَتَذُوقُواْ ٱلسُّوٓءَ بِمَا صَدَدتُّمۡ عَن سَبِيلِ ٱللَّهِ وَلَكُمۡ عَذَابٌ عَظِيمٞ
English translation: And (do) not take your oaths (as) a deception between you lest should slip a foot after it is firmly planted and you would taste the evil for what you hindered from (the) way (of) Allah and for you (is) a punishment great
Transliteration: wala tattakhidhu aymanakum dakhalan baynakum fatazilla qadamun ba'da thubutiha watadhuqu al-sua bima sadadttum an sabili al-lahi walakum adhabun azimun