וַיִּגַּ֥שׁ הַפְּלִשְׁתִּ֖י הַשְׁכֵּ֣ם וְהַעֲרֵ֑ב וַיִּתְיַצֵּ֖ב אַרְבָּעִ֥ים יֽוֹם׃ (פ)
And the Philistine drew near morning and evening, and presented himself forty days.
Rashi on I Samuel
Morning and evening. Our Rabbis said, to prevent them from reciting 'shema.'9See Maseches Sotah 42b.