Rejection of worldly compensation for preaching

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."