"The punishment of those who wage war against Allah and His Messenger, and strive with might and main for mischief through the land is: execution, or crucifixion, or the cutting off of hands and feet from opposite sides, or exile from the land: that is their disgrace in this world, and a heavy punishment is theirs in the Hereafter;" - Quran 5:33 (read more)

"O Allah's Apostle! We asked you for mounts, but you took an oath that you would not give us any mounts; we think that you have forgotten your oath.' He said, 'It is Allah Who has given you mounts. By Allah, and Allah willing, if I take an oath and later find something else better than that. then I do what is better and expiate my oath.'" - Sahih Bukhari 7:67:427 (read more)

"It is obligatory to distribute one's zakat among eight categories of recipients (O: meaning that zakat goes to none besides them), one-eighth of the zakat to each category... The seventh category is those fighting for Allah, meaning people engaged in Islamic military operations for whom no salary has been allotted in the army roster (O: but who are volunteers for jihad without remuneration)." - Ahmad ibn Naqib al-Misri