Language:
كتاب الجهاد والسير
56  
Fighting for the Cause of Allah (Jihaad)
(110)
Chapter: To give a Bai'a for not to flee during a battle
(110)
باب الْبَيْعَةِ فِي الْحَرْبِ أَنْ لاَ يَفِرُّوا
Sahih al-Bukhari 2962, 2963

Narrated Mujashi:

My brother and I came to the Prophet (ﷺ) and I requested him to take the pledge of allegiance from us for migration. He said, "Migration has passed away with its people." I asked, "For what will you take the pledge of allegiance from us then?" He said, "I will take (the pledge) for Islam and Jihad."

حَدَّثَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ، سَمِعَ مُحَمَّدَ بْنَ فُضَيْلٍ، عَنْ عَاصِمٍ، عَنْ أَبِي عُثْمَانَ، عَنْ مُجَاشِعٍ ـ رضى الله عنه ـ قَالَ أَتَيْتُ النَّبِيَّ صلى الله عليه وسلم أَنَا وَأَخِي فَقُلْتُ بَايِعْنَا عَلَى الْهِجْرَةِ‏.‏ فَقَالَ ‏"‏ مَضَتِ الْهِجْرَةُ لأَهْلِهَا ‏"‏‏.‏ فَقُلْتُ عَلاَمَ تُبَايِعُنَا قَالَ ‏"‏ عَلَى الإِسْلاَمِ وَالْجِهَادِ ‏"‏‏.‏
Reference : Sahih al-Bukhari 2962, 2963
In-book reference : Book 56, Hadith 173
USC-MSA web (English) reference : Vol. 4, Book 52, Hadith 208
  (deprecated numbering scheme)