Dear all,
So far, I'm not aware of Whitefield's sources-- meaning he could have gotten this from another means-- but he also could have adapted it for his own use, we know he did that for other hymns. But there's about a decade gap between the two, which leaves room for ambiguity. The C. P. M. version does also contain couplets not found in Seagrave's original.
Sincerely,
A. J. Higgins