Furthermore, the Greek construction Apekrithe ... kai eipen auto ("answered and said to him") is a common idiom in the New Testament. This idiom always precedes a statement directed to the referent of the dative auto ("to him"). In other words, the statement "answered and said" refers to the referent signified by the indirect object ("to him") which in this context would be Jesus Christ. There is no lexical support in any of the standard Greek references (BAGD, M&M, and Louw & Nida) where this idiom is to be taken as a relative address, as not addressing the object that the pronoun auto points to, but to someone else. There is no grammatical support in any of the standard grammars for claiming that such a construction is to be understood as referring to someone other than the addressee of the indirect object.
As one writer and apologist put it:
…There are 108 occurrences of a form of EIPON followed by AUTW(i) in the NT. 74 are EIPEN AUTW(i). 23 occur with a form of APOKRINOMAI. Ten of these are preceded by APEKRITHE. John uses EIPEN AUTW(i) 17 times. I checked all 108 occurrences. In every case, the words following AUTW(i) were addressed to the referent of AUTW(i). In addition, there are 127 examples of AUTW(i) preceded by a form of LEGW (20 combined with a form of APOKRINOMAI), and in every case I checked (about half), I did not find a single example where the person addressed was OTHER THAN the referent of AUTW(i). (Robert Hommel, Robert and MS on John 20:28; online source)
To help illustrate Hommel’s point we provide references where the words eipen auto, or their varying forms, are used in John:
They came to John and said to him (eipan auto), ‘Rabbi, that man who was with you on the other side of the Jordan—the one you testified about—well, he is baptizing, and everyone is going to him." John 3:26
"When he inquired as to the time when his son got better, they said to him (eipon oun auto), ‘The fever left him yesterday at the seventh hour.’ Then the father realized that this was the exact time at which Jesus had said to him (eipan auto), ‘Your son will live.’ So he and all his household believed." John 4:52-53
"Later Jesus found him at the temple and said to him (eipen auto), ‘See, you are well again. Stop sinning or something worse may happen to you.’" John 5:14
"Jesus’ brothers said to him (eipon oun pros auton), ‘You ought to leave here and go to Judea, so that your disciples may see the miracles you do.’" John 7:3
"‘You are not yet fifty years old,’ the Jews said to him (eipon oun hoi Ioudaioi pros auton), ‘and you have seen Abraham!’" John 8:57
"The third time he said to him, ‘Simon son of John, do you love me?’ Peter was hurt because Jesus asked him (eipen auto) the third time, ‘Do you love me?’ He said, ‘Lord, you know all things; you know that I love you.’" John 21:17
"Jesus said this to indicate the kind of death by which Peter would glorify God. Then he said to him (eipon legei auto), ‘Follow me!’" John 21:19
The above references show that eipen auto are addressed to the referent of the pronoun auto. This conclusively proves that Thomas’ confession was directed to Jesus, that John deliberately used the Greek words eipen auto in order to show that Thomas was directly addressing Jesus as his Lord and God.
From:
https://answering-islam.org/Responses/O ... thomas.htm