Al-Kāfi - The Book of Jihad (Serving in the Army)

3.Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad ibn ‘Isa from Ali ibn al-Hakam from Muthanna’ from Fitr ibn Khalifah from Muhammad ibn Ali ibn Al-Husayn from his father, recipients of divine supreme covenant, who has said the following: “’Amir al-Mu’minin (a.s.), has said, ‘The Messenger of Allah, O Allah, grant compensation to Muhammad and his family worthy of their services to Your cause, has said, “If one defends a community of Muslims in the matters of their water or fire, paradise becomes necessary (allotted) for him.’” جهول - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (18/398))