Take your time.
Don't rush into it. /Don't rush into anything.
There's no reason/need to hurry/rush.
Don't be in such a hurry/rush.
Don't be so impatient.
We have plenty of time.
Take it easy.
No need to rush yourself.
What's the rush/hurry/emergency?
Why are you in such a rush/hurry?
Why the big hurry?
A: Don't worry, take your time.
B: I'm glad we left early, so we wouldn't have to rush.
A: Calm down. What's the rush?
B: Sorry, I'm just excited.
A: Take your time deciding. Don't rush into anything.
B: Thanks. I'll be sure and consider everything you mentioned.
A: Slow down, patience is virtue.
B: Yeah, well, silence is golden. Be quiet.
A: I'll be done soon.
B: No hurry. Just let me know when you are finished.