Answer
(Fatwa: 1055/1000=D/1429)
It is necessary to invite non-Muslims as well to Eiman. Muslims are invited to make them know Islamic rulings and do good deeds so that their beliefs may be stronger and they get rewards in the Hereafter and save themselves from the Hell. While, the purpose of preaching to non-Muslims is to inspire them towards Islam and make them embrace Islam. It is essential to preach both the groups. Those saying that it is not compulsory to preach non-Muslims are not right to say this.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband