John was cleansed of original sin in his mother’s womb:
Luke1.13
"your wife Elizabeth will bear you a son, and you shall call his name John. 14 And you will have joy and gladness, and many will rejoice at his birth, 15 for he will be great before the Lord. And he must not drink wine or strong drink, and he will be filled with the Holy Spirit, even from his mother’s womb. 16 And he will turn many of the children of Israel to the Lord their God, 17 and he will go before him in the spirit and power of Elijah, to turn the hearts of the fathers to the children, and the disobedient to the wisdom of the just, to make ready for the Lord a people prepared.”
Luke 1:41
“And it came to pass, that when Elizabeth heard the salutation of Mary, the infant” – filled, like the mother, with the Holy Ghost – “leaped for joy in her womb”, as if to acknowledge the presence of his Lord. Then was accomplished the prophetic utterance of the angel that the child should “be filled with the Holy Ghost even from his mother’s womb”.
Now as the presence of any sin whatever is incompatible with the indwelling of the Holy Ghost in the soul, it follows that at this moment John was cleansed from the stain of original sin.