What was Ananias's sin as Peter identified it?
Peter identified Ananias's sin as lying to the Holy Spirit. He kept back part of the price of the land while pretending to give the whole amount. Peter said Satan filled his heart to deceive, and that Ananias had not lied to men but to God.
Les explains that Ananias and Sapphira sold a possession, like Barnabas, but kept part of the proceeds. Peter asked why Satan filled his heart to lie to the Holy Ghost and keep back part of the price. Peter said the land was Ananias's own; he didn't have to give it, but he lied and conceived this in his heart, lying not to men but to God. Les notes this wasn't a big deal by ordinary standards, but it illustrates Kingdom circumstances where death is possible for horrendous rebellion against the King.