1 Cor 16:2

16:2 On the first day of every week. The reference is to Sunday, the day on which the resurrected Lord met with His disciples (John 20:19, 26; cf. also “the Lord’s day” in Rev. 1:10). Acts 20:7 indicates that the early Christians met on Sunday “to break bread” (part of their worship), and it would have been appropriate to designate that day for collecting the offering.