Luke 1

As Luke testifies that he is one of the believers and one -

"...having had perfect understanding of all things from the very first..." (New Testament | Luke 1:3)

...explains the resources from which his record is substantiated writing -

"Forasmuch as many have taken in hand to set forth in order a declaration of those things which are most surely believed among us,
2 Even as they delivered them unto us, which from the beginning were eyewitnesses, and ministers of the word..." (New Testament | Luke 1:1 - 2)

It interpret that to mean that not only does his record rely upon his own experience, but "written" testimonies or in a sense, affidavits from those wwho were also eyewitnesses as well as the Savior's ministers.

One of the greatest testimonies that I would believe was a handwritten testimony was that of the inspired words of Mary to Elizabeth -

"...My soul doth magnify the Lord,
47 And my spirit hath rejoiced in God my Saviour.
48 For he hath regarded the low estate of his handmaiden: for, behold, from henceforth all generations shall call me blessed.
49 For he that is mighty hath done to me great things; and holy is his name.
50 And his mercy is on them that fear him from generation to generation.
51 He hath shewed strength with his arm; he hath scattered the proud in the imagination of their hearts.
52 He hath put down the mighty from their seats, and exalted them of low degree.
53 He hath filled the hungry with good things; and the rich he hath sent empty away.
54 He hath holpen his servant Israel, in remembrance of his mercy;
55 As he spake to our fathers, to Abraham, and to his seed for ever."

What a marvelous testimony from not only an "eyewitness", but as a key player in the great plan of redemption.

(New Testament | Luke 1:46 - 55)