6:19 Say: "What thing is most weighty in evidence?" Say: "Allah is Witness between me and you: this Qur'an hath been revealed to me by inspiration that I may warn you and all whom it reaches. Can ye possibly bear witness that besides Allah there is another god?" Say: "Nay! I cannot bear witness!" Say: "But in truth He is the One Allah and I truly am innocent of (your blasphemy of) joining others with Him.
Invite people to good for you will get as many rewards as earned by those people who listen to you and follow the advice without anything being deducted from their reward. (Bukhari & Muslim)