Could you tell me which one of the following sentences is correct?

a) I didn't say you can go now.
b) I didn't say you could go now.

I often hear a be spoken instead of b. But I wonder why, because sentence a is not grammatically correct with the usage of present tense 'you can go now' after the verb 'didn't'. Should we write sentence a as follow?

a modified) I didn't say "you can go now".

Or should we keep sentence a intact as it is correct? :-s
The textbook version should be "I didn't say you could go now", but in ordinary everyday conversation you may hear either one. This is not a sentence you would encounter in formal writing - in either form. The technically correct version of a) is:

I didn't say, "You can go now".

Emotion: smile
Thank again, CalifJim for your thorough reply.Emotion: big smile