Sheikh Ahmad al-Qâdî, research fellow at al-Imam University
It is not permissible to bury a Muslim in a non-Muslim graveyard.
This is in accordance with the practice of all Muslims from the time of the Prophet (peace be upon him) up until today. There is consensus on this issue derived from the practice of the Muslims.
Allah says: “If anyone contends with the Messenger even after guidance has been plainly conveyed to him, and follows a way other than the way of the people of faith, we shall leave him in the way he has chosen, and land him in Hell, and what an evil refuge it is.” [Sûrah al-Nisâ’: 115]
Assigning special graves for the Muslims is the way of the people of faith.
Bashîr b. al-Khassâsiyyah said: “I was walking with the Prophet (peace be upon him) when he passed by the graves of the Muslims. He said: “A great evil has been avoided by these people.” Then he passed by graves of the polytheists and said: “So much good has been missed out by these people.” [Sunan al-Nasâ’î (2048)]
And Allah knows best.
Source: Islam Today