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:
Muslims living in a pluralistic society should attend the funerals of their non-Muslim neighbors and colleagues to establish good relations.
Responding to your question, Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
We have no information on whether the Prophet Muhammad (peace be upon him) attended the funeral of his uncle Abu Talib.
However, we have reports of the Prophet’s companions and others attending the funerals of their relatives and non-Muslim neighbors. Furthermore, Islam also teaches us to share the joys and sorrows of our neighbors, whether Muslims or non-Muslims.
Therefore, based on such principles and the overall spirit of Islam, eminent scholars have ruled that Muslims living in a pluralistic society should attend the funerals of their non-Muslim neighbors and colleagues to establish good relations.
Furthermore, Islam also teaches us to reciprocate kindness with kindness; if Muslims were to stay away from such occasions, that would be offensive and rude on our part, especially since they will be attending Muslim funerals and extending condolences.
For more, see this section: Muslim non-Muslim Relations
Almighty Allah knows best.