Is it permissible for a Muslim to send condolences to the family, on the death of a Christian friend/colleague or a neighbor? If so is there any authentic evidence from the life of the Prophet (SAW) that he did that?
It is perfectly all right to do so, Islam commands us to be good to all people, and establish good neighborliness, reciprocating kindness with kindness, and recognizing the good in all people. Islam is all about justice and compassion; God commands us to be steadfast in upholding these virtues at all times. We are told, “O you who believe! Be steadfast witnesses for Allah in equity; and let not hatred of any people make you swerve from justice. Deal justly; that is nearer to God-fearing….” (Qur’an: 5: 8).
The Qur’an further tells us that there are among the Christians those who are full of love and compassion: “…And We placed compassion and mercy in the hearts of those who followed him (Jesus)…” (Qur’an: 57: 27). And we are also told, “…And you will find the nearest of them in affection to those who believe (to be) those who say: “We are Christians.” That is because there are among them priests and monks, and because they are not proud.” (Qur’an: 5: 82).
For instance, the late Pope John Paul 11 was undoubtedly known to all people with these qualities. Islam teaches us to recognize the good and virtue wherever they are found; and shun and abhor vice and immorality whoever practices them. Pope John Paul stood for justice and spoke against unjust, and immoral wars, and occupations, and extended and opened his arms to receive people of all faiths including Muslims; that is why as numerous Muslim scholars throughout the world have stated: In John Paul 11’s death we have lost a very good friend.
Prophetic precedents for reciprocating kindness with kindness and his magnanimity even with his foes are too numerous to count. He visited non-Muslims who were sick, he was extremely generous with his food and provisions to all of his neighbors including Muslims and non-Muslims; he welcomed the Christian delegation in his mosque and served them, he extolled the pact of virtue that the pagans had formed in pre-Islamic times, and said that he would gladly hasten to join to any similar ventures in Islam, no matter who takes the initiative. We also know from the traditions that the Prophet, peace be upon him, stood up to honor the funeral procession of a Jew. Inspired by these and other precedents, his companions used to attend the funerals of non-Muslims, including those of the People of the Book.
In conclusion, we are certainly allowed to extend condolences to our friends among Christians and others who have lost their family member or friend or a leader of their faith. We are also allowed to attend their funerals and memorials in order to extend our sympathies to the bereaved.