Levítico 5:13 Midrash: Sifra

9) (In respect to a lamb, it is written (Vayikra 5:6) lit.,) "from his sin"; (in respect to a bird, Vayikra 5:10,) "from his sin," (and, in respect to the tenth of an ephah, Vayikra 5:13,) "on (i.e., in addition to) his sin." What is the intent of this? (The intent is that) One may bring from (the monies he set aside to) the sanctuary [hekdesh]: for a lamb, a goat-kid; for a goat-kid, a lamb; for a lamb or a goat-kid, turtle-doves or young pigeons; for turtle-doves or young pigeons, a tenth of an ephah.

10) (Vayikra 5:13): "And the Cohein shall make atonement for him, for his sin that he has sinned, of one of these." What is the intent of this ("of these")? For I might think: "The most stringent of them (tumah of the sanctuary and its consecrated objects) should be subject to lamb or goat-kid; the less stringent (a court-mandated oath), to a bird; the least stringent (an oath of "pronouncement"), to the tenth of an ephah. It is therefore, (to negate this) written "of one of these" — to equate the least stringent to the most stringent vis-à-vis lamb and goat-kid, and the most stringent to the least stringent vis-à-vis the tenth of en ephah.

10) How so? If he set aside (monies for) a lamb or a goat-kid and he became poor, he may bring a bird (and use the remainder for mundane purposes — thus, "from" the monies). If he became poorer, he may bring a tenth of an ephah. If he became richer, he may (add money and) bring a bird. If he became richer he may (add money and) bring a lamb or a goat-kid (— thus, "on, i.e., in addition to). If he set aside a lamb or a goat-kid and it became unfit — he may bring, from its monies, a bird, (this, too, being subsumed in "from his sin.") If he set aside the bird and it became unfit, he may not bring from its monies the tenth of an ephah (but he purchases from his own funds either a bird or a tenth of an ephah), for there is no redemption for a bird, (but only for a beast, viz. Vayikra 27:11). This (in summary) is the intent of "from his sin," "from his sin," "on his sin."