Indeed, visiting the graves of non-Muslims is permitted for reflection. It is reported that the Prophet (peace and blessings be upon him) asked Allah if he could seek His forgiveness for his mother. He was not allowed to do so, but he was permitted to visit her grave.
Muslims should respect the graves of non-Muslims just as they do of their own brothers and sisters. The Islamic point of view does not differentiate between the grave of a Muslim or a non-Muslim. Graves should be treated in the light of the Quranic verse: “Surely we have honored the children of Adam…” (Al-‘Israa‘: 70) The application of this verse is so general to include Muslims and non-Muslims. In this context, we recall the incident that the Prophet (peace and blessings be upon him) stayed behind, after the Battle of Badr, to supervise the burial of all the unbelievers who had been killed in battle.