Scriptural source for the lost son story
As mentioned in another answer the story as written is published in at least one book by Thich Nhat Hanh. The following is copied from Being Peace, it's slightly more elaborate than the version you posted (e.g. &quot;velvet bag&quot; instead of &quot;little bag&quot;) but with many of the same phrases:




Thay doesn't attribute a source for this story.
The next story on the page of stories which you linked to, i.e. Angry Buddha, is attributed to Being Peace -- so I suppose that probably is where they found the Lost Son story too.
I gather that the Vietnamese tradition is eclectic so in theory Thay might have gathered that story from anywhere, but I think the content or 'moral' of the story suggests it probably is from the Mahayana or Zen tradition.