Gajasur's Demand

Everyone keenly listens to Ganesh Ji's birth story and how Mahadev had to deal with Gajasur, one of his biggest devotees. Garud gets worried thinking of Parvati who went to meet Shiva on Kailasa. Gajasur's 'tapasya' pays off and Mahadev visits him, but his demand shocks Mahadev. What did he ask for?