Narrated from Aisha (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever makes a vow to obey Allah, let him obey Allah; and whoever makes a vow to disobey Allah, let him not disobey Him."
Hadith Referenceمسند الإمام الشافعي / كتاب النذور / 1044
Hadith Takhrijاخرجه البخاري، الأيمان والنذور، باب النذر في الطاعة، وما انفقتم من نفقة أو نذر تم من نذر (6696) ، (6700)۔