Regex for devision class number

Hello!
Can you please tell me what regular expression can be used to divide a multi-digit number/decimals into class numbers with non-breaking spaces

Only thing that worked looks very strange and it's not multipurposal.

E.g. for 9-digit number I used Find&Replace function

123456789

Find what: ([0-9])([0-9])([0-9])([0-9])([0-9])([0-9])([0-9])([0-9])([0-9])

Replace with: $1$2$3$ 4$5$6$ 7$8$9

This one could be used, but it absolutely useless with decimals