וְהָיָה֙ כִּ֣י הִרְבְּתָ֔ה לְהִתְפַּלֵּ֖ל לִפְנֵ֣י יְהוָ֑ה וְעֵלִ֖י שֹׁמֵ֥ר אֶת־פִּֽיהָ׃
And it came to pass, as she prayed long before the LORD, that Eli watched her mouth.
Read midrashic interpretation of I Samuel 1:12: and classical rabbinic exegesis.