Musar zu Bereschit 18:29

Therefore one should not neglect submitting to lashes at least once a month. This is what our forefather Avraham was alluding to when he said to Hashem, “Perhaps there will be found there forty [righteous men]” (Bereishis 18:29). As the Zohar (1:104b) clarifies the meaning: “Perhaps there will be found there individuals who submit themselves to the forty lashes,” to which Hashem responded, “I will not destroy, etc.”