Modeh Ani

When was Modeh Ani instituted?

Shalom!

Thank you for your question.

Indeed, immediately upon awakening, even prior to washing one's hands, one is to recite Modeh Ani. This is in order to thank G-d for having retuned our soul to us after a night’s sleep. So too, it is to remind us that G-d is watching us and that we should promptly get out of bed to begin serving Him with the ritual handwashing and the morning prayers. Moden Ani should be recited even while still sitting or lying in bed.

As per your question, indeed, Modeh Ani is not found in the Talmud and was not recited in Talmudic times. At that time they would recite “Elokai Neshama” upon awakening and this was permissible because there was no “spirit of impurity” at that time. In fact, there is no mention of Modeh Ani at all in the Rambam who simply writes that one recites “Elokai Neshama” upon awakening.

It seems that the first source to record a custom of reciting Modeh Ani upon awakening is the work "Seder Hayom" from about the year 1600. There is also mention of it in the Siddur Yaavetz about 100 years later. Even through we are concerned for the spirit of impurity nowadays, it is permitted to recite Modeh Ani before washing one’s hands as there is no mention of one of the seven names of G-d and therefore clean hands are not required.

Rabbeinu Yonah in Brachos 60b; Shulchan Menachem 1:1; Be’er Heitev 1:5; Mishna Berura 1:8.