What should we do?

My husband and I adopted a little girl. It wasn’t planned. Her mom was on drugs and didn’t want her going to the state. So she asked if we would adopt and we decided to. We’ve had her since she was 3 days old and now she’s 18 months old. The problem is that me and my husband can’t agree on when/if to tell her she’s adopted. I feel like we should start telling her now that way she always knows and doesn’t feel like our relationship is built on lies. My husband in the beginning didn’t want me to tell her at all. Now he wants me to wait until she’s older. I don’t feel right keeping that from her. It feels like lying. Everybody has a right to know where they came from. Any adoptive parents have any advice? What did you do? Or anybody that was adopted as a child would you have rather grew knowing or would you have rather found out when you were older?