Midrasch zu Mischlej 10:30

Another comment on The tongue of the righteous is as choice silver (Prov. 10:30). This refers to the Holy One, blessed be He, who chose the tongue of Moses when he told him: When thou takest the sum (to obtain forgiveness). What is written above concerning this very matter? And Aaron shall make atonement upon the horns of it once in the year (Exod. 30:10). After Israel had sinned, the Holy One, blessed be said to Moses: Go, atone for them. Whereupon Moses replied: Did You not say to me once in the year? The Holy One, blessed be He, replied: Go lift up their heads (obtain forgiveness) now. Then Moses said to the Holy One, blessed be He: Master of the Universe, when they do good let them be at rest, but when they are without merit, as though that were possible, let them be forgiven once a year in order that the Day of Atonement may come and atonement be made for them, as it is said: For on that day shall atonement be made for you (Lev. 16:30).