Acts 8:36

‘And as they went on the way, they came to a certain water, and the eunuch says, “Look, here is water. What hinders me from being baptised?'

The eunuch accepts Philip's explanation, given by the power of the Spirit, as convincing and seeing an abundant spring of water with its surrounding pond he asks why, in that case, he might not baptised. Philip's explanation would have included reference to baptism.

A later copier, seized with the idea of the need at baptism for a confession of faith, or possibly finding a marginal note to that effect which he felt must be a part of the text, adds here, ‘and Philip said, “If you believe with all your heart you may”, and he answered and said, “I believe that Jesus Christ is the Son of God”.' (Compare Acts 9:20; 1 John 4:15; 1 John 5:5). The words are undoubtedly an addition but the intent is right. Philip would hardly have baptised the eunuch without being convinced of the genuineness of his faith.