Is it permissible for a Muslim nurse to participate in collecting money as a farewell gift for a Christian colleague at the hospital?

Kindness to all people and creation is commendable. It is permissible for a Muslim to cooperate with a non-Muslim to aid someone in need or to support an oppressed person. There is no sin in giving money to Christians as a gift, unless it is used for something unlawful. However, it is more virtuous to spend money on needy Muslims.