Lemma 38.8.4. Let $R$ be a ring. Let $I \subset R$ be an ideal. Let $R \to S$ be a ring map, and $N$ an $S$-module. Assume
$R$ is a Noetherian ring,
$S$ is a Noetherian ring,
$N$ is a finite $S$-module,
$N$ is flat over $R$, and
for any prime $\mathfrak q \subset S$ which is an associated prime of $N \otimes _ R \kappa (\mathfrak p)$ where $\mathfrak p = R \cap \mathfrak q$ we have $IS + \mathfrak q \not= S$.
Then the map $N \to N^\wedge $ of $N$ into the $I$-adic completion of $N$ is universally injective as a map of $R$-modules.