Disinterestedness in da'wah (calling to Islam)

قُلْ مَآ أَسْـَٔلُكُمْ عَلَيْهِ مِنْ أَجْرٍ إِلَّا مَن شَآءَ أَن يَتَّخِذَ إِلَىٰ رَبِّهِۦ سَبِيلًا

Say, "I do not ask of you for it any payment - only that whoever wills might take to his Lord a way."