וְחַנָּ֗ה הִ֚יא מְדַבֶּ֣רֶת עַל־לִבָּ֔הּ רַ֚ק שְׂפָתֶ֣יהָ נָּע֔וֹת וְקוֹלָ֖הּ לֹ֣א יִשָּׁמֵ֑עַ וַיַּחְשְׁבֶ֥הָ עֵלִ֖י לְשִׁכֹּרָֽה׃
װאָרום חנה, זי האָט גערעדט אין איר האַרצן; בלױז אירע ליפּן האָבן זיך געשאָקלט, אָבער איר קָול האָט זיך ניט געהערט; און עלי האָט זי גערעכנט פֿאַר אַ שיכּורער.
Rashi
Eili thought she was drunk. Because they were not accustomed to praying silently.
Metzudat David
And Channah: But, "Channah was praying in her heart" - meaning to say, in a whisper, as if she was speaking to her heart, so it was not audible to Eli.
Radak
Spoke in her heart: It is like its translation [in Targum Yonatan], "she prayed in her heart." Meaning to say, she concentrated [with] her heart in prayer.