Sahih Muslim 15 c
It is narrated on the authority of Jabir that a man once said to the Messenger of Allah (ﷺ):
Shall I enter Paradise in case I say the obligatory prayers, observe the (fasts) of Ramadan and treat that as lawful which has been made permissible (by the Shari'ah) and deny myself that what is forbidden, and make no addition to it? He (the Holy Prophet) replied in the affirmative. He (the inquirer) said: By Allah, I would add nothing to it.
وَحَدَّثَنِي سَلَمَةُ بْنُ شَبِيبٍ، حَدَّثَنَا الْحَسَنُ بْنُ أَعْيَنَ، حَدَّثَنَا مَعْقِلٌ، - وَهُوَ ابْنُ عُبَيْدِ اللَّهِ - عَنْ أَبِي الزُّبَيْرِ، عَنْ جَابِرٍ، أَنَّ رَجُلاً، سَأَلَ رَسُولَ اللَّهِ صلى الله عليه وسلم فَقَالَ أَرَأَيْتَ إِذَا صَلَّيْتُ الصَّلَوَاتِ الْمَكْتُوبَاتِ وَصُمْتُ رَمَضَانَ وَأَحْلَلْتُ الْحَلاَلَ وَحَرَّمْتُ الْحَرَامَ وَلَمْ أَزِدْ عَلَى ذَلِكَ شَيْئًا أَأَدْخُلُ الْجَنَّةَ قَالَ ‏
"‏ نَعَمْ ‏"‏ ‏.‏ قَالَ وَاللَّهِ لاَ أَزِيدُ عَلَى ذَلِكَ شَيْئًا ‏.‏