וַתִּקַּ֞ח שָׂרַ֣י אֵֽשֶׁת־אַבְרָ֗ם אֶת־הָגָ֤ר הַמִּצְרִית֙ שִׁפְחָתָ֔הּ מִקֵּץ֙ עֶ֣שֶׂר שָׁנִ֔ים לְשֶׁ֥בֶת אַבְרָ֖ם בְּאֶ֣רֶץ כְּנָ֑עַן וַתִּתֵּ֥ן אֹתָ֛הּ לְאַבְרָ֥ם אִישָׁ֖הּ ל֥וֹ לְאִשָּֽׁה׃
Então Sarai, esposa de Avram, tomou Hagar, a serva Mimitzrayim, após dez anos de Avram residir na terra de Canaã, e a deu a Avram, seu marido, para ser sua esposa.
Sforno
לשתות העם, that the people could drink. The unusual construction is similar to Genesis 16,3 לשבת אברהם.
Or HaChaim
If we find that even Sarai did use the term "wife" in connection with Hagar (Genesis 16,3), she countermanded such an interpretation by saying that she should be a wife only vis-a-vis Abraham. She was to remain a slave-woman vis-a-vis herself. Compare my commentary there.
Redeeming Relevance; Genesis
Sarai the wife of Avram took Hagar the Egyptian, her maidservant, at the end of ten years of Avram’s dwelling in the land of Canaan, and she gave her to Avram her husband as a wife. He came to Hagar and she became pregnant. She saw that she had become pregnant and her mistress became light in her eyes. Sarai said to Avram, “My injury is upon you – I gave you my maidservant into your lap, she saw that she became pregnant and I became light in her eyes; God should judge between us.…” Avram said to Sarai, “Here is your maidservant in your hand – do to her what is good in your eyes.” Sarai afflicted her and she ran away from her.