And the 99th prohibition is that we are forbidden from bringing an offering without salt.

The source of this prohibition is G‑d's statement1 (exalted be He), "Do not leave out the salt of your G‑d's covenant [from your meal offerings]." This warning not to leave out the salt implies that it is prohibited to bring an unsalted offering. One who does bring an unsalted offering — whether an animal or a meal offering — is punished by lashes.

The details of this mitzvah are explained in the seventh chapter of Zevachim.2