Sincerity in Da'wah (Islamic Preaching)

وَمَآ أَسْـَٔلُكُمْ عَلَيْهِ مِنْ أَجْرٍ ۖ إِنْ أَجْرِىَ إِلَّا عَلَىٰ رَبِّ ٱلْعَـٰلَمِينَ

And I do not ask you for it any payment. My payment is only from the Lord of the worlds.