Question Summary:
Reference for the Hadith on Abu Bakr (radhiyAllahu ‘anhu) giving instructions to Usamah bin Zaid (radhiyAllahu ‘anhu) upon dispatching his army

Question Detail:

Could you give me a reference for the following Hadith. The final instructions Abu Bakt Siddique RA gave to gave to Usama RA to the Muslim army were: "Do not be deserters, nor be guilty of disobedience. Do not kill an old man, a woman or a child. Do not injure date palms and do not cut down fruit trees. Do not slaughter any sheep or cows or camels except for food. You will encounter persons who spend their lives in monasteries. Leave them alone and do not molest them."

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
The advices Abu Bakr (radhiyAllahu ‘anhu) gave to Usamah bin Zaid (radhiyAllahu ‘anhu) upon dispatching his army are as follows:
يا أيها الناس قفوا أوصيكم بعشر فاحفظوها عني: لا تخونوا، ولا تغلوا ولا تغدروا ولا تمثلوا، ولا تقتلوا طفلا صغيرا، ولا شيخا كبيرا، ولا امرأة، ولا تعقروا نخلا، ولا تحرقوه، ولا تقطعوا شجرة مثمرة، ولا تذبحوا شاة ولا بقرة ولا بعيرا إلا لمأكلة، وسوف تمرون بأقوام قد فرغوا أنفسهم في الصوامع فدعوهم وما فرغوا أنفسهم له، وسوف تقدمون على أقوام يأتونكم بآنية فيها ألوان الطعام، فإذا أكلتم منها شيئا بعد شيء فاذكروا اسم الله عليه، وسوف تلقون أقواما قد فحصوا أوساط رؤوسهم وتركوا حولها مثل العصائب، فاخفقوهم بالسيوف خفقا.... 
Translation: O people, halt! I counsel you with ten (things). Preserve them from me. Do not betray (a trust), nor embezzle (war booty), nor commit treachery, nor mutilate, nor kill a small child nor an elderly man, nor a woman. Do not uproot a date-palm, nor burn it, and do not cut a tree bearing fruit and do not slaughter a goat, cow or camel except for consumption. You will soon pass by people who have devoted themselves to the monasteries so leave them to what they have devoted themselves to. And you will soon come upon people who will present to you vessels containing various shades of food, so when you eat morsel after morsel from them, mention the name of Allah over it. And you will soon meet such people who have shaven the middle of their heads and have left its surroundings like a turban, strike them with the sword……. 
The above mentioned narration is found in Kanzul ‘Ummaal quoting from Ibn ‘Asaakir. [1]
 
 
And Allah Ta’āla Knows Best
Fahad Abdul Wahab
Student Darul Iftaa
USA
Checked and Approved by,
Mufti Ebrahim Desai                                                                                                                                                                                                                
www.Daruliftaa.net