What is the ruling regarding a son whose father disowned him in writing before his death, but the wife denied this claim; does he inherit or not?

The child is attributed to the owner of the bed (the husband), and the child's lineage is only denied through li'an (oath of condemnation). If the husband disowns the child but does not perform li'an with his wife during his lifetime, then the child is attributed to him and inherits from him. A message left by the husband to deny lineage has no legal effect.