This tells me only of these alone. Whence do I derive (the same for) the other unclean animals? It follows a fortiori, viz.: If these (the aforementioned), which have signs of cleanliness, are forbidden by negative commandment, then the other unclean beasts, which have no signs of cleanliness — how much more so should eating them be forbidden by negative commandment! In sum: Camel, hare, coney, and swine are forbidden by Scripture, and the other unclean beasts, a fortiori. Their positive commandment is Scripture; their negative commandment, a fortiori.
Which Animals Are Forbidden and How We Know
Sifrei Devarim 101:10