A man came to the Prophet (PBUH) and said: My sister vowed to perform Hajj and she died. The Prophet (PBUH) said: Had there been a debt on your sister, would you have paid it? The man replied: Yes. So, the Prophet (PBUH) said: -a debt to- Allah is worthier of fulfillment.

O Messenger of Allah, I vowed in pre-Islamic times of ignorance to perform i'tikaf (ritual seclusion) in the Sacred Mosque for a night, so he said to him: Fulfill your vow.