We know that when Chazal present p’sukim from the Torah, N’viim, and K’suvim, it generally follows this order; p’sukim from the Torah are mentioned first. That being the case, why did Chazal place Az Yashir at the end of P’sukei D’Zimrah, which are primarily p’sukim from T’hilim – part of the K’suvim category? Az Yashir should have logically been placed first. This question is asked by the Zohar (Parshas T’rumah 131:2) and quoted by the Aruch HaShulchan (siman 52:1).