Full Idea
Many, not without reason, laugh at those ridiculous fancies of the schools, that rashly take away all extensions from spirits, whether souls or angels, and then dispute how many of them booted and spurred may dance on a needle's point at once.
Gist of Idea
The schools said spirits lack extension, and wonder how many could dance on a needle's point
Source
Henry More (Immortality of the Soul [1659], III.2.1), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 17.3
Book Reference
Pasnau,Robert: 'Metaphysical Themes 1274-1671' [OUP 2011], p.360
A Reaction
This famous idea originated with William Chillingworth. More's version is the classic one. Pasnau cites Aquinas Summa 1a 52.3 as discussing the actual question (and says this couldn't happen).