משנה על תרומות 11:2

As for trees: the pear and the crustumenian pear, the medlar and azarolus, do not constitute kilayim one with the other. The apple and the crab-apple, or the peach and almond, or the jujube and rimin, even though they are similar one to the other, they nevertheless constitute kilayim one with the other.

[A non-priest drank] honey of dates, wine of apples, vinegar from winter grapes, and all other kinds of fruit juice of terumah: Rabbi Eliezer makes him liable to repay their value and the fifth; But Rabbi Joshua exempts from the fifth. Rabbi Eliezer declares [these] susceptible to uncleanness as liquids. Rabbi Joshua says: the sages have not enumerated seven liquids as those that count spices, but rather they stated: seven liquids make things susceptible to uncleaness, whereas all other liquids do not make susceptible.