Is it permissible for someone who has vowed to donate a small amount daily for a religious purpose to pay the entire sum at once to fulfill his vow, for fear of not being able to continue?

It is permissible to hasten the fulfillment of a vow and offer it all at once, if it is of the nature of charities. The scholars have stated the permissibility of offering a vow before its appointed time in matters akin to charities. It is stated in Asna al-Matalib: "If one vows a charity, not a fast or a prayer, at a specific time, it is permissible to hasten its fulfillment, just as one would hasten zakat, given that each of them is a financial act of worship."