(64) Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi)
كتاب المغازى
(17) Chapter: The Ghazwa of Uhud
(17) باب غَزْوَةِ أُحُدٍ
Sahih al-Bukhari 4046 

Narrated Jabir bin `Abdullah:

On the day of the battle of Uhud, a man came to the Prophet (ﷺ) and said, "Can you tell me where I will be if I should get martyred?" The Prophet (ﷺ) replied, "In Paradise." The man threw away some dates he was carrying in his hand, and fought till he was martyred .

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مُحَمَّدٍ، حَدَّثَنَا سُفْيَانُ، عَنْ عَمْرٍو، سَمِعَ جَابِرَ بْنَ عَبْدِ اللَّهِ ـ رضى الله عنهما ـ قَالَ قَالَ رَجُلٌ لِلنَّبِيِّ صلى الله عليه وسلم يَوْمَ أُحُدٍ أَرَأَيْتَ إِنْ قُتِلْتُ فَأَيْنَ أَنَا قَالَ ‏ "‏ فِي الْجَنَّةِ ‏"‏ فَأَلْقَى تَمَرَاتٍ فِي يَدِهِ، ثُمَّ قَاتَلَ حَتَّى قُتِلَ‏.‏
Reference : Sahih al-Bukhari 4046
In-book reference : Book 64, Hadith 92
USC-MSA web (English) reference : Vol. 5, Book 59, Hadith 377
  (deprecated numbering scheme)