Greetings
It is mostly from Gnostic sources which was prior to the formation of Christianity.

Y'shua grew up in Kemet. How do you think he had such knowledge and wisemind when he is presented as an adult in the Gospels?

Moses was an initiate while in Kemet. So it is not a stretch to sight how Y'shua followed in the trodition of Moses.

There is a book called "The Jesus Papers" that mention his time in Kemet.

Dr. Ben Yochanan wrote about Y'shua and the Mystery schools as well.

Just to make you aware, it was the Greeks who coined the term "mystery" school because they could not grasp the teachings. It was not such a mystery to Afrikan people. It was considered high science along with spirituality.

Peace