The Holy Prophet (may peace be upon him) has given clear instructions about the behaviour of the Muslim army. He observed:
"Set out for Jihad in the name of Allah and for the sake of Allah. Do not lay hands on the old verging on death, on women, children and babes. Do not steal anything from the booty and collect together all that falls to your lot in the battlefield and do good, for Allah loves the virtuous and the pious."
So great is the respect for humanly feelings in Islam that even the wanton destruction of enemy's crops or property is strictly forbidden. The righteous Caliphs followed closely the teachings of Allah and those of His Apostle in letter and spirit the celebrated address which the first Caliph Abu Bakr (Allah be pleased with him) gave to his army while sending her on the expedition to the Syrian borders is permeated with the noble spirit with which the war in Islam is permitted. He said:
"Stop, O people, that I may give you ten rules for your guidance in the battlefield. Do not commit treachery or deviate from the right path. You must not mutilate dead bodies. Neither kill a child, nor a woman. nor an aged man. Bring no harm to the trees, nor burn them with fire, especially those which are fruitful. Slay not any of the enemy's flock. save for your food. You are likely to pass by people who have devoted their lives to monastic services; leave them alone"
It is said that once at the time of conquest, a singing girl was brought to al-Muhajir b. Abu Umayya who had been publicly singing satirical poems about Hadrat Abu Bakr. Muhajir got her hand amputated. When the Caliph heard this news, he was shocked and wrote a letter to Muhajir in the following words:
"I have learnt that you laid hands on a woman who had hurled abuses on me, and, therefore, got her hand amputated. God has not sought vengeance even in the case of polytheism, which is a great crime. He has not permitted mutilation even with regard to manifest infidelity. Try to be considerate and sympathetic in your attitude towards others in future. Never mutilate, because it is a grave offence. God purified Islam and the Muslims from rashness and excessive wrath. You are well aware of the fact that those enemies fell into the hands of the Messenger of Allah (may peace be upon him) who had been recklessly abusing him; who had turned him out of his home; and who fought against him, but he never permitted their mutilation."
Another letter written by hadrat 'Umar the Second Caliph, which is addressed to Sa'd b. Abu Waqqas, speaks eloquently of the noble spirit with which the Muslims have bear exhorted to take up arms:
"Always search your minds and hearts and stress upon your men the need of perfect integrity and sincerity in the cause of Allah. There should be no material end before them in laying down their lives. but they abould deem it a means whereby they can please their Lord and entitle them. selves to His favour: such a spirit of selflessness should be inculcated in the minds of those who unfortunately lack it. Be firm in the thick of the battle as Allah helps man according to the perseverance that he shows in the cause of His faith and he would be rewarded in accordance with the spirit of sacrifice which he displays for the sake of the Lord. Be careful that those who have been entrusted to your care receive no harm at your hands and are never deprived of any of their legitimate rights."