How to replace a whitespace before number using Replace method?

How to replace a whitespace before number using Replace method?

I want to replace a whitespace before a digit using java method
ReplaceAll? How should i create a regex to make it?
Here is an example:
I want to change:
John 9:50
Steve 12:30
Luke Peter 14:44
To:
John\t9:50
Steve\t12:30
Luke Peter\t14:44