Take the ward with you and travel to Moonglade, to the Stormrage Barrow Dens. Within the southernmost of the Stormrage Barrow Dens, watched over by the dreamwardens, you will find Clintar Dreamwalker.
Administer the potion and watch over him while he wakes. He'll be extremely vulnerable as his spirit reunites with his body and he certainly won't recognize you. Declare yourself to him as soon as he comes around, <name>. He will need your help to gather the relics for the ceremony.