A.T. Robertson Commentary Acts 8:20

"But Peter said unto him, Thy silver perish with thee, because thou hast thought to obtain the gift of God with money." — Acts 8:20 (ASV)

Perish with thee (συν σο ειη εις απωλειαν). Literally, Be with thee for destruction. Optative for a future wish. The use of εις with the accusative in the predicate is especially common in the LXX. The wish reveals Peter's indignation at the base offer of Simon. Peter was no grafter to accept money for spiritual power. He spurned the temptation. The natural meaning of Peter's language is that Simon was on the road to destruction. It is a warning and almost a curse on him, though verse 22 shows that there was still room for repentance.

To obtain (κτασθα). To acquire. Usual meaning of the present tense (infinitive middle) of κταομα.