Genesis 16:6

But Abram said unto Sarai, Behold, thy maid is in thy hand; do to her as it pleaseth thee. And when Sarai dealt hardly with her, she fled from her face.

Abram said ... Behold, thy maid is in thy hand. Abram being a man of peace, as well as affectionately disposed toward his wife, left her to settle these broils in her own way. In all households where concubinage exists, the principal wife retains her supreme authority over the inferior ones; and in cases where a slave is brought into the relation with her master that Hagar held to Abram, the maid-servant remains in her former position unchanged; or although some more attentions may be paid to her, she is as much subject to the absolute control of her mistress as before. Sarai, left by Abram to act at discretion, exerted her full authority.

And ... Sarai dealt hardly with her - [Hebrew, watª`anehaa (H6031), oppressed, afflicted, or would oppress, afflict her.] The word implies that, in her violent bursts of resentment, Sarai frequently had, or threatened to have, recourse to blows, until at length Hagar, perceiving the hopelessness of maintaining the unequal strife, resolved to escape from what had become to her in reality, as well as in name, a house of bondage.