Answer
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
Once a mosque donation is handed over to the mosque administration, it cannot be taken back by the giver.
In his response to your question, Prof. Dr. Monzer Kahf, Professor of Islamic Finance and Economics at Qatar Faculty of Islamic Studies, states:
There is a great reward for charity. We read in the Quran:
Indeed, the men who practice charity and the women who practice charity and [they who] have loaned Allah a goodly loan – it will be multiplied for them, and they will have a noble reward. (Al-Hadid 57:18)
Those who spend their wealth [in Allah ‘s way] by night and by day, secretly and publicly – they will have their reward with their Lord. And no fear will there be concerning them, nor will they grieve. (Al-Baqarah 2:274)
There is nothing wrong with taking back charity before it is handed over to the poor person.
However, once a donation or gift is handed over to its recipient, it cannot be taken back by the giver.
Prophet Muhammad (peace be upon him) said: “One who takes back his gift (which he has already given) is like a dog that swallows its vomit.” (Al-Bukhari)
Umar ibn al-Khattab said, “If someone gives a gift to strengthen ties with a relative or as charity, he cannot have it returned…” (Malik)
Almighty Allah knows best.