The greatest right of God against you is that you worship Him without associating anything with Him. When you do that with sincerity (ikhlas), He has made it binding upon Himself to give you sufficiency in the affair of this world and the next.

فأَمَّا حَقُّ اللهِ الأَكْبَرُ فَإنَّكَ تَعْبُدُهُ لا تُشْرِكُ بهِ شَيْئاً، فَإذَا فَعَلْتَ ذَلِكَ بإخلاصٍ جَعَلَ لَكَ عَلَى نَفْسِهِ أَنْ يَكفِيَكَ أَمْرَ الدُّنْيَا وَالآخِرَةِ وَيَحْفَظَ لَكَ مَا تُحِبُّ مِنْهَما.