Where has Christ promised that we are as certainly washed with His blood and Spirit as with the water of Baptism?

Heidelberg Catechism

Question 71. Where has Christ promised that we are as certainly washed with His blood and Spirit as with the water of Baptism?

Answer. In the institution of Baptism, which says: “Go therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit.[1] He that believes and is baptized shall be saved; but he that believes not shall be damned.”[2] This promise is also repeated where Scripture calls Baptism the washing of regeneration[3] and the washing away of sins.[4]

[1] Mt 28:19; [2] Mk 16:16; [3] Tit 3:5; [4] Acts 22:16