Reference for Pesachim 177:17

א"ר יוחנן כדי לזרזן במצות קאמר

- Rather it is on account of the [blood] applications: for whereas the Passover-offering [requires] one application, the peace-offering [requires] two, which are four.<span class="x" onmousemove="('comment',' The blood was applied to the north-east and the south-west corners of the altar, thus making it appear that the four corners were besprinkled; v. Zeb. 53b.');">¹⁴</span>

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