Midrasch zu Tehillim 86:11

... Another opinion "may my heart be complete in Your laws", this is concerning the law of Pesach and the law of the Red Cow. Why? Because the two of them are similar one to the other, regarding one it is stated "these are the laws of the Pesach" and regarding the other is it stated "these are the laws of the Torah". And you can't know which one is more important than the other. It is like the parable of two distinguished ladies that were walking, and they looked similar. How would you know which one is more distinguished? The one whom the other accompanies to her house and walks after her. So too, regarding Pesach it is written "law" and regarding the Red Cow it is written "law", and which one is more important? The Cow, since Pesach needs it, as it says "And they will take for the ritually impure from the ashes of the burnt sacrifice" (Numbers 19:17)...