Language:
كتاب فرض الخمس
57  
One-fifth of Booty to the Cause of Allah (Khumus)
(8)
Chapter: The statement of the Prophet saws: "Booty has been made legal for you Muslims."
(8)
بَابُ قَوْلِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «أُحِلَّتْ لَكُمُ الْغَنَائِمُ»
Sahih al-Bukhari 3121

Narrated Jabir bin Samura:

Allah's Messenger (ﷺ) said, "When Khosrau is ruined, there will be no Khosrau after him; and when Caesar is ruined, their will be no Caesar after him. By Him in Whose Hands my life is, you will spend their treasures in Allah's Cause."

حَدَّثَنَا إِسْحَاقُ، سَمِعَ جَرِيرًا، عَنْ عَبْدِ الْمَلِكِ، عَنْ جَابِرِ بْنِ سَمُرَةَ ـ رضى الله عنه ـ قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏ "‏ إِذَا هَلَكَ كِسْرَى فَلاَ كِسْرَى بَعْدَهُ، وَإِذَا هَلَكَ قَيْصَرُ فَلاَ قَيْصَرَ بَعْدَهُ، وَالَّذِي نَفْسِي بِيَدِهِ، لَتُنْفَقَنَّ كُنُوزُهُمَا فِي سَبِيلِ اللَّهِ ‏"‏‏.‏
Reference : Sahih al-Bukhari 3121
In-book reference : Book 57, Hadith 30
USC-MSA web (English) reference : Vol. 4, Book 53, Hadith 350
  (deprecated numbering scheme)