Status of a tree existing on land before it is designated as a mosque.
General Chapter
Al-Mughni
Book of Endowments (Awqaf) and Donations
Primary text
If a tree already exists on the land when the owner dedicates it as a mosque, there is no objection. Ahmad permitted this in one instance. Regarding its fruit, Ahmad stated in the narration of Abu Talib concerning the Nabq tree that it should not be sold but given for the consumption of the Muslims and the residents of the locality. This is understood because when the owner designated the land as a mosque while the tree was present, he endowed both the land and the tree, without specifying its use, making it an absolute endowment whose use was unspecified, which can revert to the poor according to one narration.
Supporting text
If the owner explicitly states, 'This is an endowment for the mosque,' then its fruit should be sold and the proceeds directed towards the mosque's needs, similar to an endowment made for the mosque while situated elsewhere.