Adam Clarke on 1 Samuel 25:39

To take her to him to wife - It is likely that he had heard before this that Saul, to cut off all his pretensions to the throne, had married Michal to Phalti; and this justified David in taking Abigail or any other woman; and, according to the then custom, it was not unlawful for David to take several wives. By his marriage with Abigail, it is probable he became possessed of all Nabal's property in Carmel and Maon.