كتاب الإيمان
Chapter: To pay Al-Khumus (one-fifth of the war booty to be given in Allah's Cause) is a part of faith
باب أَدَاءُ الْخُمُسِ مِنَ الإِيمَانِ
Sahih al-Bukhari 53

Narrated Abu Jamra:

I used to sit with Ibn 'Abbas and he made me sit on his sitting place. He requested me to stay with him in order that he might give me a share from his property. So I stayed with him for two months. Once he told (me) that when the delegation of the tribe of 'Abdul Qais came to the Prophet, the Prophet (ﷺ) asked them, "Who are the people (i.e. you)? (Or) who are the delegate?" They replied, "We are from the tribe of Rabi'a." Then the Prophet (ﷺ) said to them, "Welcome! O people (or O delegation of 'Abdul Qais)! Neither will you have disgrace nor will you regret." They said, "O Allah's Messenger (ﷺ)! We cannot come to you except in the sacred month and there is the infidel tribe of Mudar intervening between you and us. So please order us to do something good (religious deeds) so that we may inform our people whom we have left behind (at home), and that we may enter Paradise (by acting on them)." Then they asked about drinks (what is legal and what is illegal). The Prophet (ﷺ) ordered them to do four things and forbade them from four things. He ordered them to believe in Allah Alone and asked them, "Do you know what is meant by believing in Allah Alone?" They replied, "Allah and His Apostle know better." Thereupon the Prophet (ﷺ) said, "It means:

1. To testify that none has the right to be worshipped but Allah and Muhammad is Allah's Messenger (ﷺ).

2. To offer prayers perfectly

3. To pay the Zakat (obligatory charity)

4. To observe fast during the month of Ramadan.

5. And to pay Al-Khumus (one fifth of the booty to be given in Allah's Cause).

Then he forbade them four things, namely, Hantam, Dubba,' Naqir Ann Muzaffat or Muqaiyar; (These were the names of pots in which Alcoholic drinks were prepared) (The Prophet (ﷺ) mentioned the container of wine and he meant the wine itself). The Prophet (ﷺ) further said (to them): "Memorize them (these instructions) and convey them to the people whom you have left behind."

حَدَّثَنَا عَلِيُّ بْنُ الْجَعْدِ، قَالَ أَخْبَرَنَا شُعْبَةُ، عَنْ أَبِي جَمْرَةَ، قَالَ كُنْتُ أَقْعُدُ مَعَ ابْنِ عَبَّاسٍ، يُجْلِسُنِي عَلَى سَرِيرِهِ فَقَالَ أَقِمْ عِنْدِي حَتَّى أَجْعَلَ لَكَ سَهْمًا مِنْ مَالِي، فَأَقَمْتُ مَعَهُ شَهْرَيْنِ، ثُمَّ قَالَ إِنَّ وَفْدَ عَبْدِ الْقَيْسِ لَمَّا أَتَوُا النَّبِيَّ صلى الله عليه وسلم قَالَ ‏"‏ مَنِ الْقَوْمُ أَوْ مَنِ الْوَفْدُ ‏"‏‏.‏ قَالُوا رَبِيعَةُ‏.‏ قَالَ ‏"‏ مَرْحَبًا بِالْقَوْمِ ـ أَوْ بِالْوَفْدِ ـ غَيْرَ خَزَايَا وَلاَ نَدَامَى ‏"‏‏.‏ فَقَالُوا يَا رَسُولَ اللَّهِ، إِنَّا لاَ نَسْتَطِيعُ أَنْ نَأْتِيَكَ إِلاَّ فِي شَهْرِ الْحَرَامِ، وَبَيْنَنَا وَبَيْنَكَ هَذَا الْحَىُّ مِنْ كُفَّارِ مُضَرَ، فَمُرْنَا بِأَمْرٍ فَصْلٍ، نُخْبِرْ بِهِ مَنْ وَرَاءَنَا، وَنَدْخُلْ بِهِ الْجَنَّةَ‏.‏ وَسَأَلُوهُ عَنِ الأَشْرِبَةِ‏.‏ فَأَمَرَهُمْ بِأَرْبَعٍ، وَنَهَاهُمْ عَنْ أَرْبَعٍ، أَمَرَهُمْ بِالإِيمَانِ بِاللَّهِ وَحْدَهُ‏.‏ قَالَ ‏"‏ أَتَدْرُونَ مَا الإِيمَانُ بِاللَّهِ وَحْدَهُ ‏"‏‏.‏ قَالُوا اللَّهُ وَرَسُولُهُ أَعْلَمُ‏.‏ قَالَ ‏"‏ شَهَادَةُ أَنْ لاَ إِلَهَ إِلاَّ اللَّهُ وَأَنَّ مُحَمَّدًا رَسُولُ اللَّهِ، وَإِقَامُ الصَّلاَةِ، وَإِيتَاءُ الزَّكَاةِ، وَصِيَامُ رَمَضَانَ، وَأَنْ تُعْطُوا مِنَ الْمَغْنَمِ الْخُمُسَ ‏"‏‏.‏ وَنَهَاهُمْ عَنْ أَرْبَعٍ عَنِ الْحَنْتَمِ وَالدُّبَّاءِ وَالنَّقِيرِ وَالْمُزَفَّتِ‏.‏ وَرُبَّمَا قَالَ الْمُقَيَّرِ‏.‏ وَقَالَ ‏"‏ احْفَظُوهُنَّ وَأَخْبِرُوا بِهِنَّ مَنْ وَرَاءَكُمْ ‏"‏‏.‏
Reference : Sahih al-Bukhari 53
In-book reference : Book 2, Hadith 46
USC-MSA web (English) reference : Vol. 1, Book 2, Hadith 51
  (deprecated numbering scheme)