I made a vow to buy a chandelier for a mosque with a certain sum of money. Is it permissible to donate that money to the mosque-affiliated clinic as it needs beds and medical equipment? Can I donate that money or some of it to another mosque that needs maintenance and depends on donations and individual efforts?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

If one vows to do an act of obedience, then he is obliged to fulfill it. The Prophet, sallallaahu ‘alayhi wa sallam, said: "Whoever vowed to obey Allaah, the Exalted, must obey Him..." [Al-Bukhari and Muslim]

Hence, if the mosque to which you vowed to donate that money is still in need of a chandelier, it is incumbent on you to buy it and offer it to the mosque. However, if the mosque does not need it, then there is nothing wrong in donating this money to another mosque. If the income of the mosque-affiliated clinic is spent on the mosque, then there is nothing wrong in donating the vowed money to this clinic, otherwise, it is impermissible to donate the money that was vowed to the mosque to it.

Allaah Knows best.