مَنِ احْتَبَسَ فَرَسًا فِي سَبِيلِ اللَّهِ إِيمَانًا بِاللَّهِ وَتَصْدِيقًا بِوَعْدِهِ، فَإِنَّ شِبَعَهُ وَرِيَّهُ وَرَوْثَهُ وَبَوْلَهُ فِي مِيزَانِهِ يَوْمَ الْقِيَامَةِ
Translation: Whoever keeps a horse dedicated in Allah’s cause, out of faith in Allah and trust in His promise, will have even its nourishment, drinking, dung, and urine counted in their scale on the Day of Resurrection.
Source: البخاري
احْتَبَسَ فَرَسًا refers to keeping a horse dedicated for a particular purpose. إِيمَانًا بِاللَّهِ وَتَصْدِيقًا بِوَعْدِهِ expresses faith and trust in Allah’s promise. فَإِنَّ emphasizes the result, and فِي مِيزَانِهِ means “in their scale of deeds.”
The narration describes reward for sustaining a horse dedicated in Allah’s cause for a specific purpose. Feeding it, giving it water, and attending to its ordinary needs are part of the reward described.