The Muslim All Blacks midfielder's trip south means he will miss the Auckland-based franchise's Super Rugby match against the Highlanders at Eden Park on Friday night.
Assistant coach Tom Coventry said the coaches thought it would be a good idea, even before Williams made the request.
"We were going to ask Sonny if he'd like to make the decision to go.
"We were all in agreeance, it was a pretty short conversation.
"We all knew how hard he took it, so it was a simple decision to make."