Answer: Gospel of John
In the Gospel of John, the apostle Thomas (taoma twin in Aramaic) is reported as Dydimus, which in koine Greek (the Greek spoken at the time the gospel was written) also means "twin."
As an example, we can read in this mentioned gospel its 11th chapter and 16th verse (according to the New International Version)
:
"Then Thomas (also known as Didymus) said to the rest of the disciples, 'Let us also go, that we may die with him.' "
