The earliest sources on the Battle of Kosovo, which generally favour the cult of
Prince Lazar, do not mention Miloš or his assassination of the sultan. The assassination itself is first recorded by
Deacon Ignjatije on 9 July 1389, only 12 days after the battle. The assassination of sultan Murad and one of his sons (
Yakub Çelebi) was also mentioned in the instructions of the
Venetian Senate issued to Andrea Bembo on 23 July 1389, although Venetians were uncertain if news about the assassination were true. On 1 August 1389 King
Tvrtko I of Bosnia (r. 1353–1391) wrote a letter to
Trogir to inform its citizens about the Ottoman defeat. Victory over the Turks () was also reported by
Coluccio Salutati (died 1406), Chancellor of Florence, in his letter to King Tvrtko, dated 20 October 1389, on behalf of the Florentine Senate. The killer is not named but he is described as one of twelve Christian noblemen who managed to break through the Ottoman ranks: :"Fortunate, most fortunate are those hands of the twelve loyal lords who, having opened their way with the sword and having penetrated the enemy lines and the circle of chained camels, heroically reached the tent of Amurat [Murad] himself. Fortunate above all is that one who so forcefully killed such a strong vojvoda by stabbing him with a sword in the throat and belly. And blessed are all those who gave their lives and blood through the glorious manner of martyrdom as victims of the dead leader over his ugly corpse." Scholars consider many details in Tvrtko's letter to be fanciful, including the symbolic number 12. In 1402, an anonymous Catalan author assigned Murad's death to a Hungarian knight. The knight might have been related to Lazar through marriage and had sent a Hungarian contingent to the battle. In the legend, Miloš Obilić was Lazar's son-in-law; in reality, Lazar had a Hungarian son-in-law. The assassin's first appearance in Serbian sources is in the biography of
Stefan Lazarević, Lazar's son, by
Constantine the Philosopher, written in the 1440s. The hero, still anonymous, is described as a man of noble birth whom envious tongues had sought to defame before the prince. To prove his loyalty and courage, he left the front line on the pretext of being a deserter, seized the opportunity to stab the sultan to death and was killed himself shortly afterwards. The initial phase of ignominy and its redemption by a courageous plot of slaying the sultan are narrative ingredients which would become essential to the Serbian legend as it evolved in later times. The loss of the Sultan also made an impression on the earliest Ottoman sources. They usually describe how Murad was unaccompanied on the battlefield and an anonymous Christian who had been lying among the corpses stabbed him to death. In the early 15th century, for instance, the poet Ahmedi writes that "[s]uddenly one of the Christians, who was covered in blood and apparently hidden among the enemy dead, got up, rushed to Murad and stabbed him with a dagger."
Halil İnalcık explained that one of the most important contemporary Ottomans sources about the Battle of Kosovo is the 1465 work of
Enveri (). İnalcık argued that it was based on the testimony of a contemporary eyewitness of the battle, probably Hoca Omer, an envoy sent by the Sultan to Lazar before the battle. In this work Enveri explains that before he became a Serbian nobleman, Miloš (Miloš Ban is how İnalcık rendered the name in Enveri's text) was a Muslim at the Sultan's court who deserted Ottomans and abjured Islam. The Sultan allegedly called him to return to his service many times. Enveri explains that although Miloš always promised to return, he never did. According to this account, when Lazar was captured, Miloš approached the Sultan who was riding a black stallion and said:
"I am Miloš Ban, I want to go back to my Islamic faith and kiss your hand." When Miloš came close to the Sultan, he struck him with the dagger hidden in his cuff. The Sultan's men cut Miloš into pieces with swords and axes. One historian from
Edirne,
Oruc Bey, explains the lack of protection by saying that the army was preoccupied with pursuing the enemy in rear flight and introduces an element of deception: the Christian "had promised himself as a sacrifice and approached Murad, who was sitting alone on his horse. Pretending he wished to kiss the Sultan's hand, he stabbed the Sultan with a sharp dagger." Since about the late 15th century, Greek sources also begin to record the event. The Athenian scholar
Laonicus Chalcocondyles (d.
c. 1490) claims to draw on Greek traditions when he refers to Murad's killer as
Miloes, "a man of noble birth [... who] voluntarily decided to accomplish the heroic act of assassination. He requested what he needed from Prince Lazar, and then rode off to Murad's camp with the intention of presenting himself as a deserter. Murad, who was standing in the midst of his troops before the battle, was eager to receive the deserter. Miloes reached the Sultan and his bodyguards, turned his spear against Murad, and killed him." Writing in the second half of the same century,
Michael Doukas regarded the story as worthy of inclusion in his
Historia Byzantina. He relates how the young nobleman pretended to desert the battle, was captured by the Turks and professing to know the key to victory, managed to gain access to Murad and kill him. In 1976, Miodrag Popović suggested that the narrative elements of secrecy and stratagem in the Serbian tradition were all introduced from Turkish sources, seeking to defame the capabilities of their Christian opponents by attributing the death of the Murat to "devious" methods. Thomas A. Emmert agrees with him. In 1512, Ottoman historian
Mehmed Nesri wrote a detailed account of the battle that became the source for later Ottoman and Western descriptions of the battle. Nesri's account took several elements from popular Serbian tradition, and described the assassination in a way which reflected negatively on the perpetrators. ==Oral traditions==