הלכה על זבחים 40:9

From the laws of the commandment is that which they, may their memory be blessed, said (Zevachim 20b) that one who goes out of the wall of the yard requires sanctification of the hands. And that if he sanctified his hands today, he needs to go back and sanctify [them] tomorrow - even if he did not sleep the whole night - as the hands are disqualified by [passing the night]. And that the commandment is ideally to wash the face, the hands and the feet in the morning; that it is a commandment to sanctify with the water of the basin (Zevachim 22b), and that if he sanctified [his hands] from one of the serving vessels, it is fit, ex post facto - but not from a non-sacred vessel, even ex post facto. And that they do not put their hands into [the water], but we pour it over their hands - and this is also the way of honor. But we do not require this regarding the [washing] of the hands for non-sacred foods - to [wash] from a vessel and not into it. As even though we require a vessel for the [washing] for the non-sacred, and the foundation of the matter is because we found [the requirement] for a vessel by [washing] for the sanctified - nonetheless it is with the sanctified that the [Torah] excluded it, but with the non-sacred, there is no exclusion. And even though the [washing] for the non-sacred is by extension of the priestly tithe - and as they, may their memory be blessed, said (Chullin 106a), "By extension of the priestly tithe" - still we do not make them the same in all of their laws. And [so] it is enough for us to obligate [washing] and a vessel for the non-sacred - by extension of the priestly tithe - and to leave the exclusion [derived from] "from it," that is said about it in its place. And even about the priestly tithe itself, its [washing] of the hands is rabbinic; as by Torah writ, one only finds purity for the entire body at once, and that which they, may their memory be blessed, said (Chullin 106a) that the [washing] is [derived] from that which is written (Leviticus 15:11), "and he did not wash his hands, etc." - that is just a memory device (asmakhta). And so is it written in the Sefer HaMitzvot of Ramban, may his memory be blessed (see Sefer HaMitzvot LaRambam, Shoresh 1, s.v. beteshuvah hashenit).