Saint Augustine says that, "some have received the invisible sanctification without visible sacraments, and to their profit; but though it is possible to have the visible sanctification, consisting in a visible sacrament, without the invisible sanctification, it will be to no profit" (Super Levit. lxxxiv).Thus, even for these two doctors, there was an "invisible sanctification" (sanctificatio invisibilis).
Saint Thomas Aquinas says: "Since, therefore, the sacrament of Baptism pertains to the visible sanctification, it seems that a man can obtain salvation without the sacrament of Baptism, by means of the invisible sanctification."
Quoted in Thomas Aquinas Summa theologiae III q. 68, a. 2, s.c.