Waaqidi reports that during the Battle of Yarmook, one of the most senior Roman commanders by the name of Jarja stepped forward from the line of soldiers and asked to meet Hadhrat Khaalid bin Waleed رضى الله عنه. Hadhrat Khaalid رضى الله عنه went to meet him and drew so close that the necks of their horses met. 

The following conversation ensued: 

Jarja: 0 Khaalid رضى الله عنه! I want you to tell me something, but do speak the truth and do not lie because a free man never lies. Do not deceive me either because a respectable person never deceives someone who trusts him. Has Allaah given your Nabi a sword from the heavens which he has given to you by virtue of which you defeat anyone against whom you draw it? 

Hadhrat Khaalid رضى الله عنه: No 

Jarja: Then why are you called the sword of Allaah (‘Sayfullaah’)? 

Hadhrat Khaalid رضى الله عنه: Allaah sent His Nabi amongst us who preached to us.However, we expressed resentment and kept our distance from him. Even I was amongst those who treated him like a liar and ostracised him. Thereafter, Allaah seized our hearts and forelocks and guided us through him. We then pledged allegiance to him. He once said to me, ‘You are a sword from the swords of  Allaah whom Allaah has drawn against the Mushrikeen.’ He then prayed to Allaah to assist me. This is why I am called the sword of Allaah. I am therefore amongst the sternest of Muslims against the Mushrikeen. 

Jarja: 0 Khaalid رضى الله عنه! Towards what do you call? 

Hadhrat Khaalid رضى الله عنه: We call people to testify that there is none worthy of worship but Allaah and that Muhammad صلى الله عليه وسلم is Allaah’s servant and Rasul. We also call them to accept everything that Rasulullaah صلى الله عليه وسلم has brought from Allaah. 

Jarja: What about those who do not accept this? 

Hadhrat Khaalid رضى الله عنه: They will have to pay the Jizya and we will protect them. 

Jarja: What if they do not pay it? 

Hadhrat Khaalid رضى الله عنه: We then declare war against them and fight. 

Jarja: What is the status of a person who accepts what you say and enters the fold of your religion? 

Hadhrat Khaalid رضى الله عنه: We all share the same status with respect to the injunctions that Allaah has made binding on us regardless of whether we have a high social standing or not and regardless of whether we accepted Islaam earlier or later. 

Jarja: Will a person entering Islaam today have the same reward as yourself? 

Hadhrat Khaalid رضى الله عنه: Certainly! In fact, his rewards shall be greater. 

Jarja: How can such a person be rated equal to you when you have accepted Islaam before him? 

Hadhrat Khaalid  رضى الله عنه: We had no option but to accept Islaam because our allegiance was pledged while our Nabi صلى الله عليه وسلم was alive and in our midst. Revelation from the heavens would come to hid and he would recite the Qur’aan to us and show us miracles. For anyone who saw what we saw and who heard what we heard there was no option but to accept Islaam and to pledged allegiance to him. As for you people, you have not seen the miraculous events and signs (of his Nabuwaat) that we saw and heard. Therefore, whoever of you will enter this Deen with sincerity shall be better than us. 

Jarja: I swear by AIlaah that you have been’honest with me and did not deceive me either. 

Hadhrat KhaaIid رضى الله عنه:By Allaah! I have certainly spoken the truth and Allaah is Witness to the fact that ,I have responded to your questions to the best of my ability. 

Jarja then turned his shield around (an indication that he did not intend fighting) and turned to Hadhrat Khaalid رضى الله عنه saying, “Teach me Islaam.” Hadhrat Khaalid رضى الله عنه took him to his tent, poured a waterbag of water over him (to assist him to bath) and then led him as he performed two Rakaahs salaah.Thinking that the muslims were scheming something when Jarja left with Hadhrat Khaalid رضى الله عنه, the Romans launched an offensive that caught the Muslims completely by surprise. Every Muslim regiment was rooted from their position besides the Muhaamiya regiment led by Hadhrat Ikrama bin Abi Jahal رضى الله عنه and Hadhrat Haarith bin Hishaam رضى الله عنه.The Romans were already in the midst of the Muslim camp when Hadhrat Khaalid رضى الله عنه mounted his horse with Jarja following closely. The Muslims called to each other and managed to regain their foothold. The Romans were then forced to return to their base. 

Hadhrat Khaalid رضى الله عنه then gradually advanced the Muslim army until they crossed swords with the enemy. Hadhrat Khaalid رضى الله عنه and Jarja رضى الله عنه continuously fought the Romans from noon until the sun was about to set. (The fighting was so fierce that) The Muslims performed the Zuhr and Asr salaahs with indications.Jarja was mortally injured in the battle (and passed away the same day). The only salaah he therefore performed for Allaah were the two he performed with Hadhrat Khaalid . May Allaah shower His mercy on him.(1) 

Note: 

(1) Al Bidaaya wan Nihaaya (Vo1.7 Pg.12). Isaaba (Vol.1 Pg.260) contains some further commentary on the narration.