34a at the bottom
How can the gemoro kearn that the tekio of rosh hashono is with a shofar not a chatzotzro, from the posuk of: "tiku bachodesh shofar" which is a posuk in tehilim? How did they blow before they wrote tehilim?
Avrumi Hersh, London england
There are many examples of details of Mitzvos that are Mekubal mi'Sinai, a Tradition passed down from Sinai and consequently a bonafide d'Oraisa, that later became Torah she'bi'Chsav when they were written in Nevi'im or Kesuvim. Its appearance in Nach does not take away from its d'Oraisa origin. (See for example Rambam Hilchos Bi'as Mikdash 6:8).
In this case there was a Peirush Mekubal mi'Sinai that the Mitzvah on Rosh Hashanah requires a Shofar and not Chatzotzros. After Tehilim was written and the Halachah became Torah she'bi'Chsav, the Pasuk became available to serve as a proof for this Tradition.
Avraham Phillips