I believe that because of what Baha'u'llah wrote about Moses. Since I believe that Baha'u'llah was a Messenger of God and He wrote His own scriptures, whatever He wrote is the bottom line for me.
The Kitáb-i-Íqán is considered the second most important work that Baha'u'llah revealed. In it Baha'u'llah describes the succession of Prophets (Messengers) who have come to earth, and He explains something about each one. Abraham and Moses were two such Prophets. However it is important to note that just because these Prophets existed that does not mean they did everything that is recorded in the Bible. I believe that the only things we can know for certain that they did is what is in the Baha'i Writings.
“Among the Prophets was Abraham, the Friend of God. Ere He manifested Himself, Nimrod dreamed a dream. Thereupon, he summoned the soothsayers, who informed him of the rise of a star in the heaven. Likewise, there appeared a herald who announced throughout the land the coming of Abraham.
After Him came Moses, He Who held converse with God. The soothsayers of His time warned Pharaoh in these terms: “A star hath risen in the heaven, and lo! it foreshadoweth the conception of a Child Who holdeth your fate and the fate of your people in His hand.” In like manner, there appeared a sage who, in the darkness of the night, brought tidings of joy unto the people of Israel, imparting consolation to their souls, and assurance to their hearts. To this testify the records of the sacred books. Were the details to be mentioned, this epistle would swell into a book.” The Kitáb-i-Íqán, pp. 62-63
Baha'u'llah concludes that paragraph by saying that He did not wish to dwell on the past and He considers that to be a grave mistake and a grievous transgression. The reason that He said that is because we are now living in a new Day of God and we now have new scriptures that pertain to this age.
"Moreover, it is not Our wish to relate the stories of the days that are past. God is Our witness that what We even now mention is due solely to Our tender affection for thee, that haply the poor of the earth may attain the shores of the sea of wealth, the ignorant be led unto the ocean of divine knowledge, and they that thirst for understanding partake of the Salsabíl of divine wisdom. Otherwise, this servant regardeth the consideration of such records a grave mistake and a grievous transgression."
The Kitáb-i-Íqán, p. 63