Augustine of Hippo — as excerpted in the Catena Aurea on Matthew 26:39-44

“(de Cons. Ev. iii. 4.) And that none might think that He limited His Father’s power, He said not, If thou canst do it, but If it may be, or, If it be possible; as much as to say, If thou wilt. For whatever God wills can be done, as Luke expresses more plainly; for he says not, If it be possible, but If thou wilt.”