I'm not sure about the base of the home that the son bought from his mother.

Example: Mother sells home to son FMV $300,000, selling contract shows selling price $300,000
and Gift of Equity of $50,000, Son gets loan for $250,000 to complete the sales.

Question: What is son's base in the house when he goes to sell it? Is it $250,000 or $300,000?