Continuing the rant of Dasan and Aviram, they accused Moshe of deceit and refused to come. (Their words "lo naaleh" literally translate as "we will not ascend" - words that turned out to be truer than they could have imagined!)
Moshe was angered by these false accusations and he prayed to G-d not to favor the offerings of the rebels. G-d was well aware that Moshe was not guilty of nepotism or self-enrichment - he hadn't taken so much as a donkey from the people!
The next morning, Aharon, Korach and the members of Korach's rebellion all appeared at the Mishkan to offer their incense. G-d then caused His Presence to manifest.