What if one worded the vow in a vague manner, entitled a "Yad": Nedarim 7a
The requirement to fulfill such a vow begins immediately upon the declaration of the vow: Rosh HaShanah 6a Death of a Spouse for failure to fulfill a vow of charity: Succah 29b; Tos. Rosh HaShanah 6a; Tos. Zevachim 29b #1 Drought as punishment for failure to fulfill a pledge of charity: Taanit 8b
On the consequences of failing to maintain vows of charity: Succah 29b