Musar על בבא קמא 76:7

Our sages in Baba Kama 38 say that a person should always perform a מצוה at the earliest possible opportunity, because of the single night that Lot's older daughter preceded her younger sister (in sleeping with her father), she merited that the maternal founder of the Davidic dynasty Ruth was born four generations sooner than Na'amah, the future wife of Rechavam son of Solomon. G–d examines the motives of people. Although what the daughters of Lot did appears as brazen, G–d knew that their motivation was pure. It was an עבירה לשמה, a sin performed for the sake of G–d. If prompt performance of such a dubious act brings such reward in its wake, how much more must one hurry to perform those מצות promptly that are clearly means of sanctifying oneself.