See this link, page 223 http://www.fikreraza.org/books/books/bahaare-shariat-vol16[1].pdf (Bahaare Shariat Vol 16 English translation). The sale where a Muslim sells alcohol is impermissible in general and the money earned is also impermissible. The question was for whether a payment of debt to a Muslim by a Kafir who made his money from selling alcohol is permissible or not.
Imam Nawawi (RA) explicitly mentions in his commentary about the hadith against alcohol that it is haraam whether sold to a Muslim or a kafir (Al Majmu).
I don't know what comes next now, will working as a bartender in a pub be permissible as long as you are serving to a kafir?
But thats talking about Dar al Islam whilst we are discussing in Dar al Harb.