It is narrated on the authority of Mu'adh b. Jabal:

I was riding behind the Prophet (ﷺ) and there was nothing between him and me but the rear part of the saddle, when he said: Mu'adh b. Jabal: To which I replied: At your beck and call, and at your pleasure, Messenger of Allah! He moved along for a few minutes, when again he said: Mu'adh b. Jabal: To which I replied: At your beck and call, and at your pleasure, Messenger of Allah! He then again moved along for a few minutes and said: Mu'adh b. Jabal: To which I replied. At your beck and call, and at your pleasure. Messenger of Allah He, (the Prophet) said: Do you know what right has Allah upon His servants? I said: Allah and His Messenger know best. He (the Prophet) said: Verily the right of Allah over His servants is that they should worship Him, not associating anything with Him. He (the Prophet) with Mu'adh behind him, moved along for a few minutes and said: Mu'adh b. Jabal: To which I replied: At your beck and call, and at your pleasure, Messenger of Allah! He (the Prophet) said: Do you know what rights have servants upon Allah in case they do it (i. e. they worship Allah without associating anything with Him)? I (Mu'adh b. Jabal) replied: Allah and His Messenger know best. (Upon this) he (the Prophet) remarked: That He would not torment them (with the fire of Hell).

حَدَّثَنَا هَدَّابُ بْنُ خَالِدٍ الأَزْدِيُّ، حَدَّثَنَا هَمَّامٌ، حَدَّثَنَا قَتَادَةُ، حَدَّثَنَا أَنَسُ بْنُ مَالِكٍ، عَنْ مُعَاذِ بْنِ جَبَلٍ، قَالَ كُنْتُ رِدْفَ النَّبِيِّ صلى الله عليه وسلم لَيْسَ بَيْنِي وَبَيْنَهُ إِلاَّ مُؤْخِرَةُ الرَّحْلِ فَقَالَ ‏"‏ يَا مُعَاذَ بْنَ جَبَلٍ ‏"‏ ‏.‏ قُلْتُ لَبَّيْكَ رَسُولَ اللَّهِ وَسَعْدَيْكَ ‏.‏ ثُمَّ سَارَ سَاعَةً ثُمَّ قَالَ ‏"‏ يَا مُعَاذَ بْنَ جَبَلٍ ‏"‏ ‏.‏ قُلْتُ لَبَّيْكَ رَسُولَ اللَّهِ وَسَعْدَيْكَ ‏.‏ ثُمَّ سَارَ سَاعَةَ ثُمَّ قَالَ ‏"‏ يَا مُعَاذَ بْنَ جَبَلٍ ‏"‏ ‏.‏ قُلْتُ لَبَّيْكَ رَسُولَ اللَّهِ وَسَعْدَيْكَ ‏.‏ قَالَ ‏"‏ هَلْ تَدْرِي مَا حَقُّ اللَّهِ عَلَى الْعِبَادِ ‏"‏ ‏.‏ قَالَ قُلْتُ اللَّهُ وَرَسُولُهُ أَعْلَمُ ‏.‏ قَالَ ‏"‏ فَإِنَّ حَقَّ اللَّهِ عَلَى الْعِبَادِ أَنْ يَعْبُدُوهُ وَلاَ يُشْرِكُوا بِهِ شَيْئًا ‏"‏ ‏.‏ ثُمَّ سَارَ سَاعَةً ثُمَّ قَالَ ‏"‏ يَا مُعَاذَ بْنَ جَبَلٍ ‏"‏ ‏.‏ قُلْتُ لَبَّيْكَ رَسُولَ اللَّهِ وَسَعْدَيْكَ ‏.‏ قَالَ ‏"‏ هَلْ تَدْرِي مَا حَقُّ الْعِبَادِ عَلَى اللَّهِ إِذَا فَعَلُوا ذَلِكَ ‏"‏ ‏.‏ قَالَ قُلْتُ اللَّهُ وَرَسُولُهُ أَعْلَمُ ‏.‏ قَالَ ‏"‏ أَنْ لاَ يُعَذِّبَهُمْ ‏"‏ ‏.‏