Midrash sur Job 12:4

R. Idi, the father of R. Jacob b. Idi, had the habit of being on the road for three months, and one day in college. The students of the college called him "The one-day student." He soon became discouraged, applying the following verse to himself (Job 12, 4) I am one that is a laughing-stock to his neighbor, a man that called upon God, and He answered him. R. Jochanan then said to him: "I pray thee, do not cause the Rabbis to be punished [by Heaven on accoimt of you]." He thereupon lectured: (Is. 58, 2) Yet Me do they ever seek day by day, and to know My ways do they always desire. Do they then seek only by day, and not by night? This is to teach us that he who studies the Torah even one day in the year. Scripture considers it as if he had studied the whole year; and so also does the passange concerning evil compensation read (Num. 14, 34) After the number of days in which ye spied out the lands, forty days, yea, each one day for a year, shall ye bear for your iniquities, for forty years. Did they sin forty years, is it not a fact that they sinned but forty days? But this is to teach us that he who violates but one command, and this once in a year, the Scripture regards it as though he transgressed the whole year.