וָֽאֶתְנַפַּ֞ל לִפְנֵ֣י יְהוָ֗ה אֵ֣ת אַרְבָּעִ֥ים הַיּ֛וֹם וְאֶת־אַרְבָּעִ֥ים הַלַּ֖יְלָה אֲשֶׁ֣ר הִתְנַפָּ֑לְתִּי כִּֽי־אָמַ֥ר יְהוָ֖ה לְהַשְׁמִ֥יד אֶתְכֶֽם׃
Postréme, pues, delante de SEÑOR cuarenta días y cuarenta noches que estuve postrado; porque SEÑOR dijo que os había de destruir.
Mishneh Torah, Prayer and the Priestly Blessing
Prostration. After he has raised his head, subsequent to the fifth genuflection, the worshiper seats himself on the floor and "falls upon his face" and offers all the supplications he pleases. Genuflection, wherever mentioned, always refers to bending the knees. Kidah means "falling on the face" [with knees bent]. Hishtahvayah means stretching out the hands and feet, so that one is lying prone with face to the ground.