Muadh ibn Jabal Allah be pleased with him narrates that the messenger of Allah, Allah shower His peace and blessings upon him took hold of his (Muadh’s) hand and said ‘Oh Muadh! I swear by Allah, I most definitely love you, I swear by Allah I most definitely love you.’ He then said ‘I advise you oh Muadh, be sure not to leave out saying the following at the end of every Salah:

Oh Allah! Assist me in remembering You, and being grateful to You and worshiping You in a beautiful manner.

Uqbah says that Muadh advised As-sunabihiy to recite this Dua, and As-sunabihiy advised Abu Abdur Rahman.

حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ عُمَرَ بْنِ مَيْسَرَةَ حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يَزِيدَ الْمُقْرِئُ حَدَّثَنَا حَيْوَةُ بْنُ شُرَيْحٍ قَالَ سَمِعْتُ عُقْبَةَ بْنَ مُسْلِمٍ يَقُولُ حَدَّثَنِى أَبُو عَبْدِ الرَّحْمَنِ الْحُبُلِىُّ عَنِ الصُّنَابِحِىِّ
عَنْ مُعَاذِ بْنِ جَبَلٍ أَنَّ رَسُولَ اللَّهِ -صلى الله عليه وسلم- أَخَذَ بِيَدِهِ وَقَالَ يَا مُعَاذُ وَاللَّهِ إِنِّى لأُحِبُّكَ وَاللَّهِ إِنِّى لأُحِبُّكَ . فَقَالَ أُوصِيكَ يَا مُعَاذُ لاَ تَدَعَنَّ فِى دُبُرِ كُلِّ صَلاَةٍ تَقُولُ:

اللَّهُمَّ أَعِنِّى عَلَى ذِكْرِكَ وَشُكْرِكَ وَحُسْنِ عِبَادَتِكَ

وَأَوْصَى بِذَلِكَ مُعَاذٌ الصُّنَابِحِىَّ وَأَوْصَى بِهِ الصُّنَابِحِىُّ أَبَا عَبْدِ الرَّحْمَنِ.

(رواه أبو داود، باب في الاستغفار، ح/١٥٢٤)