Al-Imaam Al-Allaamah Muhammad Ibn Saalih Al-Uthaymeen (may Allaah be pleased with him) was asked:
Q. What is the ruling of the person who works with the disbelievers and what do you advise him with?
A. We advise this person, who works with the disbelievers, to seek employment that doesn't have within it the enemies of Allaah and His messenger (sallallaahu alayhi wa sallam) from those who practice a religion other than Al-Islaam. If this is easy for the person, then this is what is befitting. If this is not easy to do, then there's no sin upon him. That is because he is involved in his work and they are involved in their work. However, this is with the condition that he doesn't have in his heart love for them and an alliance. Also, he must hold fast to that which the legislation has come with in relation to the greeting with the Salaam and responding to it. Likewise, he doesn't propagate their deaths nor does he attend their funeral processions, nor does he attend their holiday celebration or greet them with the greetings connected to them.
Source: Maa-saa-il Fee al-Aqeedah pg. 108
Sisters Upon Al-Istiqaamah