English: Whence that one who vows “I undertake an oven-baked meal-offering” may not bring half cakes and half wafers? From the word “offering” — he brings one offering, and does not bring cakes and wafers together.
In Sifra / Menachos: Challos and rekikin are two distinct species of oven product. A single vow for “ma’afeh tanur” must be fulfilled with one species only, not a mixture of the two.
Type of Learning
Custom (species integrity within a single vow).
What Is Learned
Oven-baked mincha comes in two non-interchangeable forms; a vow for one form cannot be satisfied by mixing cakes and wafers.