Collected company + Eternal witness
Yes, you can add Collected Company to your hand.

It works like this:


Collected Company resolves choosing Eternal Witness
Eternal Witness is put onto the battlefield and triggers (but is not put on the stack yet)
Collected Company finishes resolving and is put into the graveyard as the last action of casting a spell
State based actions are checked and see that Eternal Witness has triggered and it's ability is put onto the stack and targets are chosen


By the time Eternal Witness' ability is on the stack and it's time to choose targets, Collected Company is in the graveyard and can be chosen to be returned to hand