Question 25: Is it lawful to ask Allaah to grant the reward of a vow to Imams? For example, is it permissible to say: “I make this vow for the sake of Allaah Whom I ask to give its reward to so-and- so?
Answer: This is a broad question. Vows are of two types: The first type is the Shar‘ee (Islaamically lawful) vow which is made with the intention of getting closer to Allaah. Making vows is basically commanded against. This is based on the reported Hadeeth in which the Prophet (peace be upon him) stated: Anyone who makes a vow by which they intend to obey Allaah, must obey Him (i.e., fulfill their vow), and anyone who makes a vow by which they intend to disobey Allaah, must not disobey Him (i.e., must not fulfill their vow). Thus, the act itself of making vows must be abandoned by a Mu’min (believer). When the Prophet (peace be upon him) was asked about vow-making, he replied: Do not make vows, for a vow prevent nothing from the Decree of Allaah. Rather, they merely cause a miser to give (Agreed upon by Al-Bukhaaree and Muslim)... read more here.