Pull a previous copy out of source control...
If you don't have your code under source control, here's the wake-up call to get it there.
You can't retrieve a previous copy from the current database. It's gone.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning