Well the references in the nt about Abraham bekieving and being accounted as righteous was about believing what God said it’s directly coming from here
“And, behold, the word of the LORD came unto him, saying, This shall not be thine heir; but he that shall come forth out of thine own bowels shall be thine heir.
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 15:4-6 KJV
“And, behold, the word of the LORD came unto him, saying, This shall not be thine heir; but he that shall come forth out of thine own bowels shall be thine heir.
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 15:4-6 KJV
Acts 7
1Then said the high priest, Are these things so? 2And he said, Men, brethren, and fathers, hearken; The God of glory appeared unto our father Abraham, when he was in Mesopotamia, before he dwelt in Charran, 3And said unto him, Get thee out of thy country, and from thy kindred, and come into the land which I shall shew thee. 4Then came he out of the land of the Chaldaeans, and dwelt in Charran: and from thence, when his father was dead, he removed him into this land, wherein ye now dwell. 5And he gave him none inheritance in it, no, not so much as to set his foot on: yet he promised that he would give it to him for a possession, and to his seed after him, when as yet he had no child.
Gen 11
31And Terah took Abram his son, and Lot the son of Haran his son's son, and Sarai his daughter in law, his son Abram's wife; and they went forth with them from Ur of the Chaldees,(Mesopotamia) to go into the land of Canaan; and they came unto Haran, and dwelt there. 32And the days of Terah were two hundred and five years: and Terah died in Haran.