In the summer months, it is very common for people to start Shabbath early. It often happens, that when someone has finished praying 'Arbith (and has accepted Shabbath), and comes out of the synagogue while it is still broad daylight, he sees his friend entering to start praying in a later Minyan.
Since it is still before the time by when one has to accept Shabbath, it is Shabbath for the one who has already prayed, but not for his friend who is going in to pray. The question is, can the man who has accepted Shabbath ask his friend (who has not), to do a Melakha (work that is not permitted on Shabbath) for him?
Rabbenu the Hida, z"l, and other Aharonim say that he can. However, the Hesed LaAlaphim, quoting the Bayith Hadash, says that it is appropriate to be strict in this matter. The Ben Ish Hai rules that in the case of a Miswah (precept), we should be lenient and not strict.
(See Ben Ish Hai, Shanah Beth, Parashath Wayera, Oth Zahn)
