I got my last answer, my next question is: Can I work with ex-Muslim (before he is Muslim now is Christian) any problem?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

If by 'working with him' the questioner means being an associate with him, then it is better for a Muslim to choose a trustworthy Muslim so that their business will be blessed with Allaah's Help and Permission. Abu Hurayrah narrated that the Prophet said: "Allaah says: "I am the third party among the two partners as long as one does not cheat the other, because if one cheats the other, I withdraw Myself from them." [Abu Daawood] Imaam Ash-Shawkaani interpreted the narration to mean: 'The meaning is that Allaah blesses the wealth of the two partners as long as one does not cheat the other, and He helps them, supports them and protects their wealth.'

A dissolute person or an apostate might cheat you or transgress the limits and bounds that exist between you and him, especially in relation to money matters. Allaah says (which means): {And, verily, many partners oppress one another, except those who believe and do righteous good deeds, and they are few.}[Quran 38: 24]. It is for this reason that the jurists disliked taking a non-Muslim as a partner or a Muslim who does not mind dealing in forbidden fields. Shaykh Zakariyyaa Al-Ansaari said: 'Partnership with non-Muslims is disliked.' For more details, please refer to Fatwa: 84460.

However, if by 'working with him' you mean that you are employed by him and do a permissible work for him, a work that does not humiliate you, and you do not help in sin then this is permissible, because in principle all transactions are permissible. It is reported in a weak narration that 'Ali, and another man from the Ansar worked for a Jew in return for some dates. However, if working with a non-Muslim entails being humiliated by him like serving him and fulfilling his needs then this is not permissible as stated by Imaam Ahmad, and in this regard, please refer to Fatwa: 84798.

Finally, you should advise this apostate and threaten him with the punishment of Allaah. In doing so, you can seek the help of pious and righteous people, and if this is of no avail, then you can take his matter to an Islamic court in your country so that they apply the religious ruling on him. For more details, please refer to Fatwa: 86009 about working with a non-Muslim.

Allaah Knows best.