In both the siddur of Rav Saadia Gaon and the seder of Rav Amram Gaon, there is a blessing in the morning, magbiah shefalim, for sitting up in bed.
Yet, it is conspicuously absent from the Rambam (Hilkhoth Tefillah 8-9), and commentators and rabbinic authorities claim that both Rav Amram and Rav Saadia later omitted it.
How can this be? Why would they do this? What happened to this blessing that seemingly was said by religious Jews for centuries?