Hold your horses
Definition 1 of 1
Pro Tip 1/3Impatience Alert
Use 'hold your horses' to caution someone who's acting rashly or impatiently. 
Hold your horses, we need to think this through before deciding.
Pro Tip 2/3Informal Tone
It's a casual phrase, suitable for everyday conversation, not formal situations. 
Hold your horses, Jack, the movie hasn't started yet.
Pro Tip 3/3Friendly Caution
The phrase can be a friendly way to tell someone to wait, without causing offence. 
Hold your horses! Your coffee will be ready in a minute.