وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ عُمَرَ بْنَ عَبْدِ الْعَزِيزِ، كَتَبَ إِلَى عَامِلٍ مِنْ عُمَّالِهِ أَنَّهُ بَلَغَنَا أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ إِذَا بَعَثَ سَرِيَّةً يَقُولُ لَهُمُ ‏"‏ اغْزُوا بِاسْمِ اللَّهِ فِي سَبِيلِ اللَّهِ تُقَاتِلُونَ مَنْ كَفَرَ بِاللَّهِ لاَ تَغُلُّوا وَلاَ تَغْدِرُوا وَلاَ تُمَثِّلُوا وَلاَ تَقْتُلُوا وَلِيدًا وَقُلْ ذَلِكَ لِجِيُوشِكَ وَسَرَايَاكَ إِنْ شَاءَ اللَّهُ وَالسَّلاَمُ عَلَيْكَ ‏"‏ ‏.‏

Yahya related to me from Malik that he had heard that Umar ibnAbd al-Aziz wrote to one of his governors, "It has been passed down tous that when the Messenger of Allah, may Allah bless him and grant himpeace, sent out a raiding party, he would say to them, 'Make yourraids in the name of Allah in the way of Allah. Fight whoever deniesAllah. Do not steal from the booty, and do not act treacherously. Donot mutilate and do not kill children.' Say the same to your armiesand raiding parties, Allah willing. Peace be upon you." Translation Not Available

Book Ref: Muwatta Imam Malik Book 21 Hadith 972
Web Ref:  Muwatta Imam Malik Book 21 Hadith 11