Sa'id bin al-Musayyab (may Allah have mercy on him) says that when Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) dispatched the armies towards Syria (Yazid bin Abi Sufyan, Amr bin al-As and Shurahbil bin Hasanah (may Allah be pleased with them)), then when they mounted, Sayyiduna Abu Bakr (may Allah be pleased with him) walked with them on foot as far as Thaniyyat al-Wada' to bid the army farewell. They said: "O successor of the Messenger of Allah! We are riding and you are on foot?" He (may Allah be pleased with him) said: "I lift these steps of mine in the path of Allah seeking reward." Then, advising the commanders, he said: "I counsel you to fear Allah. Fight in the path of Allah, and fight those who disbelieve in Allah. Allah is the helper of His religion. Do not betray the trust, do not deceive, do not show cowardice, do not spread corruption in the land, and do not disobey the orders given to you. If, Allah willing, you meet the enemy, invite them to three things. If they accept, hold your hands back from them: 1. Invite them to Islam; if they accept Islam, hold your hands back from them. Then they should be asked to move from their homes to the homes of the Muhajirun. If they do so, tell them that they will have what the Muhajirun have, and the same obligations as the Muhajirun. If, after entering Islam, they prefer their own homes to the homes of the Muhajirun, tell them that they are like the ordinary Bedouin Muslims: the rulings that apply to the believers will apply to them, and they will have no share of the fay' and the spoils of war until they fight in jihad together with the Muslims. 2. If they refuse to enter Islam, invite them to the jizyah; if they do so, accept the jizyah and hold your hands back. 3. If they refuse that, seek Allah's help against them and, if Allah wills, fight them. Do not drown palm trees nor burn them; do not cut down animals or fruit-bearing trees; do not demolish churches; and do not kill children, old men or women. You will soon find people who have confined themselves in hermitages; leave them alone with that for which they have confined themselves. And you will soon find people in the middle of whose heads Satan has made a nest; when you meet such people, strike off their necks, if Allah wills."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18125
Abdullah bin Ahmad bin Hanbal says: I heard my father say: "This hadith is munkar (rejected); I do not think any of it is (sound). This is the speech of the people of Syria." My father objected to it from Yunus as a hadith of al-Zuhri, as though, in his view, Yunus had it from someone other than al-Zuhri.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18126
Imam al-Shafi'i (may Allah have mercy on him) says: Perhaps Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) forbade cutting down fruit-bearing trees only because he had heard the Prophet (peace and blessings be upon him) say: "The Muslims will conquer the cities of Syria." Cutting down a fruit-bearing tree and leaving it are both permissible, so he chose to leave them for the sake of the Muslims, not because he considered it forbidden; for he had been present with the Prophet (peace and blessings be upon him) when the fruit trees of Banu al-Nadir, Khaybar and Ta'if were burned.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18127