كتاب الرقاق
To make the Heart Tender (Ar-Riqaq)
Chapter: The example of this world in contrast with the Hereafter
باب مَثَلِ الدُّنْيَا فِي الآخِرَةِ‏
Sahih al-Bukhari 6415

Narrated Sahl:

I heard the Prophet (ﷺ) saying, "A (small) place equal to an area occupied by a whip in Paradise is better than the (whole) world and whatever is in it; and an undertaking (journey) in the forenoon or in the afternoon for Allah's Cause, is better than the whole world and whatever is in it."

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، حَدَّثَنَا عَبْدُ الْعَزِيزِ بْنُ أَبِي حَازِمٍ، عَنْ أَبِيهِ، عَنْ سَهْلٍ، قَالَ سَمِعْتُ النَّبِيَّ صلى الله عليه وسلم يَقُولُ ‏ "‏ مَوْضِعُ سَوْطٍ فِي الْجَنَّةِ خَيْرٌ مِنَ الدُّنْيَا وَمَا فِيهَا، وَلَغَدْوَةٌ فِي سَبِيلِ اللَّهِ أَوْ رَوْحَةٌ خَيْرٌ مِنَ الدُّنْيَا وَمَا فِيهَا ‏"‏‏.‏
Reference : Sahih al-Bukhari 6415
In-book reference : Book 81, Hadith 4
USC-MSA web (English) reference : Vol. 8, Book 76, Hadith 424
  (deprecated numbering scheme)