Salaam
related fatwa :
Fatwa Question or Essay Title: Can a Muslim go to crematorium to attend the last rites of non-Muslim?
A Muslim should not follow the funeral procession or attend the funerals of a non-Muslim even if he is his colleague. This is for attending the funeral of a non-Muslim--as regards to attending the crematorium, this is even worse, as by attending the burning of the body one agrees to the falsehood that is happening as it is forbidden to burn the body of a dead person.
The answer is referenced by a passage from Ibn Taymiyya (d. 1328 C.E.). Ibn Taymiyya was asked whether or not it is permissible for Muslims who are neighbors of Christians to visit them when they are sick, or follow their funeral procession when they die; and if a Muslim who does is he sinful or not? He replied, "It is forbidden for a Muslim to follow the funeral procession of a non-Muslim, but there is no harm for him to visit him when he is sick, as by doing so there is a benefit of softening his heart to accept Islam, because if he dies as a non-Muslim, he will go to Hellfire, it is for this reason that it is not permissible to pray the funeral prayer on him."
The answer also gives a secondary reference of the opinion of some scholars who sanction the attending of funerals of non-Muslim relatives. The author mentions that there is a report from Ibn Abu Shaybah that Abu Wail said: "My mother died and she was a Christian so I came to Umar and informed him about it, so he told me: "Ride a camel and precede in the procession." However if the deceased is not a relative then it is not permissible to attend his funeral procession or attend his burial. prayer on him."
Note: Ibn Taymiyya is a medieval Syrian jurist following the Hanbali school of thought. He was born in Harran (present day Turkey) in 1263 CE and died in Damascus in 1328 CE. He wrote several treatises covering several topics which included opinions on non-Muslims. This ruling is noteworthy in that Ibn Taymiyya was also strongly was against the borrowing of any rituals and traditions from Christians and non-Muslims.
For different positions, please look under "Funeral Rites, Muslims-non Muslims Relations".*
http://www.islamopediaonline.org/fatwa/can-muslim-go-crematorium-attend-last-rites-non-muslim