The Story of Heraclius Is Confirmed and Authentic
7-10-2018 | IslamWeb
Question:
How reliable are traditional Islamic history sources exactly as accurate sources which reliably describe things like pre-Islamic Arabia? I mean for example Heraclius is said according to Islamic sources to have met Abu Sufyan or heard about Islam and responded to the Prophet(PBUH) letter to him acknowledging but other sources like Lawrence Conrad have said that outside of Islamic history sources there is no evidence Heraclius heard of Islam and these reports don't shed much historical knowledge. There's also some who claim that aside from traditional sources on Islam, much of pre-Islamic Arabia is unknown and there could be biases in Muslim accounts of it.
Answer:
All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad 
is His slave and Messenger.
First of all, you should know that the story of Heraclius, his hearing about Islam, his meeting with Abu Sufyan 
and the Prophet writing to him, was not only reported in what you so-called the traditional books of history. Rather, it was reported in the authentic books of Sunnah based on chain of narrators and the scrutiny of narrations.
This story is confirmed in Saheeh Al-Bukhaari, so it cannot be challenged as false as it is confirmed with an authentic chain of narrators.
The study of chain of narrators is the way to confirm the authenticity of the information or its untruthfulness. Indeed, the Muslim Nation is characterized by this aspect contrarily to other nations, as the Muslims set principles and rules based on which they can judge any given narration. They attached great importance to this matter and they clarified that it is among the most important parts of the religion. Some of them said: "(Studying) the chain of narrators is part of the religion, and without it, anybody would claim anything they want."
Many of those who wrote history books are trustworthy, such as At-Tabari, Ath-Thahabi, and others. However, the author of a history book reports the information that has reached him regardless of whether they are authentic or inauthentic; hence, such books include authentic, inauthentic, and even fabricated narrations.
We do not know what you meant by saying that these reports don't shed much historical knowledge.
What we know is that what these people have done by gathering this history since the beginning of creation and throughout the ages is a great effort for which they should be thanked; its importance is only denied by someone who is arrogant.
Also, accusing someone of being biased is easy and can be said by anyone, but claims need evidence.
Finally, it should be noted that a Muslim should be careful and should not to pay attention to the misconceptions of enemies. He should not investigate about them unless he is deeply rooted in Islamic knowledge, enough to distinguish between what is right and wrong and would be safe from being influenced by these misconceptions.
Allah knows best.