Whoever takes an oath to do something and then he finds a better alternative which brings him closer to Allah should do what is better in piety.
[Muslim]
Original Hadith
"عن أبي طَرِيف عدي بن حاتم -رضي الله عنه- مرفوعاً: «مَن حَلَف على يَمِين ثم رأى أَتقَى لله مِنها فَلْيَأت التَّقوَى».
[صحيح.] - [رواه مسلم.]"