Must one fulfill a vow to build a mosque on land one owns if one comes to need the value of that land after acquiring it?

If a person says something intending it as a vow (nadhr), then he is obligated to fulfill it, because a vow is established by implication (kinayah) combined with intention (niyyah). However, if he did not intend it as a vow, but merely as an announcement or a resolution, then nothing is binding upon him.