Matthew Poole and continuators on 1 Samuel 1:23

23 And Elkanah her husband said unto her, Do what seemeth thee good, tarry until thou have weaned him, onely the LORD establish his word . so the woman abode, and gave her son suck until she had weaned him.

Either, First, The word of God made known to them by Eli, above, v. 17. which being delivered by Gods High-Priest, and that in answer to his and his Wives Prayers, he took to be a kind of Oracle sent from God. But that word was already fulfilled in the Birth of a Son. Or, Secondly, Some other Word or Message from God to Elkanah or his Wife concerning Samuel; for such Revelations were frequent in those Ages of the Church, and were oft vouchsafed by God, concerning such Children as were extraordinary Persons, or in a special manner Devoted to God; as concerning Isaac, Gen. 18. and Sampson, Iudg. 13. 3, 4. and Iohn Baptist, Luk. 1. 13, 14, &c. and others. And so it might be here, though it were not mentioned before, there being many such things in Scripture omitted in their proper places, which afterwards are expressed or implyed upon other occasions. Or rather, Thirdly, It may be rendered, his matter or thing, i. e. the Business concerning the Child, that which thou hast Promised or Vowed concerning him, that he may grow up, and be accepted and employed by God in his Service; and that he, when he is fully grown, may not break thy Vow, but confirm it.