פירוש על קידושין 96:10

Abaye completely changes the situation. The husband wanted to give her a silver denar, but his agent gave her a gold denar. The first tanna in the mishnah holds that the husband did not want to betroth her with a gold denar, so she is not betrothed. R. Shimon says that the husband did not really care what coin was used for betrothal, so she is betrothed.