It's not stated in the bible. It's a Jewish tradition. I seriously doubt it because Abraham most likely learned the gospel from Shem/Noah, who were both alive during his life, while he was in Haran. It could be possible that Terah believed in the one true God and migrated with his family to Haran to learn from them
“Abraham most likely learned the gospel from Shem/Noah,”
“Now
the LORD had said unto Abram, Get thee out of thy country, and from thy kindred, and from thy father's house, unto a land that I will shew thee: and I will make of thee a great nation, and I will bless thee, and make thy name great; and thou shalt be a blessing: and I will bless them that bless thee, and curse him that curseth thee:
and in thee shall all families of the earth be blessed.
So Abram departed, as the LORD had spoken unto him; and Lot went with him: and Abram was seventy and five years old when he departed out of Haran.”
Genesis 12:1-4 KJV
“Know ye therefore that
they which are of faith, the same are the children of Abraham.
And
the scripture, foreseeing that God would justify the heathen through faith, preached before the gospel unto Abraham, saying, In thee shall all nations be blessed.
So then
they which be of faith are blessed with faithful Abraham.”
Galatians 3:7-9
“And the angel of the LORD
called unto Abraham out of heaven the second time, and said, By myself have I sworn, saith the LORD,
for
because thou hast done this thing, and hast not withheld thy son, thine only son: that in blessing
I will bless thee, and in multiplying
I will multiply thy seed as the stars of the heaven, and as the sand which is upon the sea shore; and
thy seed shall possess the gate of his enemies; and in thy seed shall all the nations of the earth be blessed;
because thou hast obeyed my voice.”
Genesis 22:15-18 KJV
“Now
to Abraham and his seed were the promises made.
He saith
not, And to seeds, as of many; but as of one, And to thy seed, which is Christ.
For
as many of you as have been baptized into Christ have put on Christ.
There is
neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for
ye are all one in Christ Jesus. And
if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise.”
Galatians 3:16, 27-29 KJV
Abraham’s children are born
by faith in Christ. Believing the gospel. Which was preached to Abraham By the lord himself who ate a meal with Abraham and visited him personally blessed and called him to leave his kin and homeland and made him promises of what God would do to reward his faith
One of those promises was made pertaining to all the world all nations and kindreds and tongues , tbat promise is Jesus Christ Gods only begotten son , who like Abraham didn’t withhold his only son from God , God also answered with his o my son being sacrificed for all sinners to have true everlasting hope of salvation from the condemnation and dominion of sin.
this part
“For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.”
John 3:16 KJV
Is because of this part
because thou hast done this thing, and hast not withheld thy son, thine only son: that in blessing
I will bless thee, and in multiplying
I will multiply thy seed as the stars of the heaven, and as the sand which is upon the sea shore; and
thy seed shall possess the gate of his enemies; and in thy seed shall all the nations of the earth be blessed;
because thou hast obeyed my voice.”
and will fulfill this part
“And he brought him forth abroad, and said, Look now toward heaven, and tell the stars, if thou be able to number them: and he said unto him, So shall thy seed be. And he believed in the LORD; and he counted it to him for righteousness.”
Genesis 15:5-6 KJV
“As for me,
behold, my covenant is with thee, and thou shalt be a father of many nations. Neither shall thy name any more be called Abram, but
thy name shall be Abraham; for a father of many nations have I made thee. And I will make thee exceeding fruitful, and
I will make nations of thee, and kings shall come out of thee. And
I will establish my covenant between me and thee and thy seed after thee in their generations for an everlasting covenant, to be a God unto thee, and to thy seed after thee.”
Genesis 17:4-7 KJV
“And
if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise.”