It is narrated from Sayyiduna Abdullah bin Abi Awfa (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Do not harm Khalid, for he is one of the swords of Allah, the Mighty and Majestic, which Allah has unleashed upon the disbelievers."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 3786