It is narrated from the Prophet of Islam (PBUH) who said: Whoever believes in Allah (SWT) and the Day of Judgment must fulfill his/her given promise [1]. It is also narrated from Imam Sadeq (AS) who said: Do not promise your brother when you are not able to fulfill it [2]. It is clear that a believer does not give a promise without being able to fulfill it and if a promise is given by a believer, according to Islamic teaching, that promise must be fulfilled.
[1] Osul Kafi, Al-Islamiyah, Vol. 2, page 364, Hadith 2.
[2] Beharul Anwaar, Beirut, Vo. 75, Page 250 and Tohaful Oqool, Page 367.
source : Shafaqna
