The Portuguese coach revealed in a press conference today that the Belgium international forgot his passport after travelling abroad when he 'shouldn't have' last week.
As a result, Hazard was dropped from the side that clinched a 3-0 win over Schalke 04 in the Champions League.
"He has reacted well, he apologised to me and the club but the apology was not accepted, something I couldn't accept but now it is over, something that doesn't exist anymore," said Mourinho. "He's selected and ready to play. Happy he's back, case over, he's a very good kid."
Hazard is expected to feature in the Blues' Premier League match against West Bromwich Albion tomorrow.