Luke 11:3

day by day, &c.--an extension of the petition in Matthew for "this day's" supply, to every successive day's necessities. The closing doxology, wanting here, is wanting also in all the best and most ancient copies of Matthew's Gospel. Perhaps our Lord purposely left that part open: and as the grand Jewish doxologies were ever resounding, and passed immediately and naturally, in all their hallowed familiarity into the Christian Church, probably this prayer was never used in the Christian assemblies but in its present form, as we find it in Matthew, while in Luke it has been allowed to stand as originally uttered.

— Jamieson-Fausset-Brown Commentary (public domain)