In this section

Historical Rules · 25 August 2017

Rule 903.9

Official source text from the 25 August 2017 Rules release

Permalink

If a commander would be exiled from anywhere or put into its owner’s hand, graveyard, or library from anywhere, its owner may put it into the command zone instead. This replacement effect may apply more than once to the same event. This is an exception to rule 614.5.

Find this number in the current Rules