Sunan an-Nasa'i 2090
It was narrated from Talhah bin 'Ubaidullah that:
a Bedouin came to the Messenger of Allah with unkempt hair and said: "O Allah has enjoined upon me of Salah." He said: "The five daily prayers, unless you do any more voluntarily." He said: "Tell me what Allah has enjoined upon me voluntarily." He said: "Tell me what Allah has enjoined upon me of fasting." He said: "Fasting the month of Ramadan, unless you do any more voluntarily." He said: "Tell me what Allah has enjoined upon me of Zakah." The Messenger of Allah told him of the laws of Islam, He said: "By the One Who has honored you, I will not do anything voluntarily, and I will not do anything voluntarily, and I will not do less than that which Allah has enjoined upon, me: The Messenger of Allah said: "He will succeed if he is sincere," or "He will enter Paradise if he is sincere."
أَخْبَرَنَا عَلِيُّ بْنُ حُجْرٍ، قَالَ حَدَّثَنَا إِسْمَاعِيلُ، - وَهُوَ ابْنُ جَعْفَرٍ - قَالَ حَدَّثَنَا أَبُو سُهَيْلٍ، عَنْ أَبِيهِ، عَنْ طَلْحَةَ بْنِ عُبَيْدِ اللَّهِ، أَنَّ أَعْرَابِيًّا، جَاءَ إِلَى رَسُولِ اللَّهِ صلى الله عليه وسلم ثَائِرَ الرَّأْسِ فَقَالَ يَا رَسُولَ اللَّهِ أَخْبِرْنِي مَاذَا فَرَضَ اللَّهُ عَلَىَّ مِنَ الصَّلاَةِ قَالَ ‏"‏ الصَّلَوَاتُ الْخَمْسُ إِلاَّ أَنْ تَطَوَّعَ شَيْئًا ‏"‏ ‏.‏ قَالَ أَخْبِرْنِي بِمَا افْتَرَضَ اللَّهُ عَلَىَّ مِنَ الصِّيَامِ قَالَ ‏"‏ صِيَامُ شَهْرِ رَمَضَانَ إِلاَّ أَنْ تَطَوَّعَ شَيْئًا ‏"‏ ‏.‏ قَالَ أَخْبِرْنِي بِمَا افْتَرَضَ اللَّهُ عَلَىَّ مِنَ الزَّكَاةِ فَأَخْبَرَهُ رَسُولُ اللَّهِ صلى الله عليه وسلم بِشَرَائِعِ الإِسْلاَمِ ‏.‏ فَقَالَ وَالَّذِي أَكْرَمَكَ لاَ أَتَطَوَّعُ شَيْئًا وَلاَ أَنْقُصُ مِمَّا فَرَضَ اللَّهُ عَلَىَّ شَيْئًا ‏.‏ فَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ أَفْلَحَ إِنْ صَدَقَ ‏"‏ ‏.‏ أَوْ ‏"‏ دَخَلَ الْجَنَّةَ إِنْ صَدَقَ ‏"‏ ‏.‏