What is the “classic” example of “mitzvas chavilas chavilas”?
Answer:
The classic example is a case where a person has two obligations, such as kiddush and birkas ha-mazon, and wishes to perform both of them by means of the same cup of wine.
He thereby “kills two birds (obligations) with one stone (cup of wine),” and this is considered disrespectful to the mitzvos.
Sources:
See Pesachim 102, and see Shulchan Aruch 271:2 and 299:4, and Mishnah Berurah.
