Genesis 16:4 - Joseph Benson’s Commentary on the Old and New Testaments

Her mistress was despised in her eyes Thus began the ill consequences of Abram's marriage to Hagar: much mischief it made presently. Hagar no sooner perceives herself with child, but she looks scornfully upon her mistress; upbraids her, perhaps, with her barrenness, and insults over her. Sarai falls upon Abram, and very unjustly charges him with the injury, suspecting that he countenanced Hagar's insolence: and as one not willing to hear what Abram had to say, she rashly appeals to God. Those are not always in the right that are most forward in appealing to God. Rash and bold imprecations are commonly evidences of guilt and a bad cause.