Source and decoding - Rosh Hashanah 17a
מַעֲבִיר רִאשׁוֹן רִאשׁוֹן, וְכֵן הִיא הַמִּדָּה. אָמַר רָבָא: וְעָוֹן עַצְמוֹ אֵינוֹ נִמְחָק. דְּאִי אִיכָּא רוּבָּא עֲוֹנוֹת — מִחֲשִׁיב בַּהֲדַיְיהוּ.
Taught the school of Rabbi Yishmael: He removes the first, the first - that is the attribute.
Taught the school of Rabbi Yishmael: He removes the first, the first - that is the attribute. Rava clarifies: the sin itself is not erased; if sins form a majority, it is counted with them. Mercy works within the balance, not by erasure.