At least a similar line from Markings:

I don't know Who — or what — put the question, I don't know when it was put. I don't even remember answering. But at some moment I did answer Yes to Someone — or Something — and from that hour I was certain that existence is meaningful and that, therefore, my life, in self-surrender, had a goal.

From: Dialogue [mailto:dialogue-bounces@lists.wedgeblade.net] On Behalf Of Karenbueno via Dialogue
Sent: Tuesday, May 08, 2018 1:14 PM
To: oe@wedgeblade.net; dialogue@lists.wedgeblade.net
Cc: Karenbueno
Subject: [Dialogue] Tracing a quote

Is there someone who can tell me the reference for the line, "there had to be someone who said yes".

I know it is from a poem, but I don't know what or where or whom.

Karen Bueno