TT #25 · Parashas Chayei Sarah · Passuk 24:14
let the maiden to whom I say, ‘Please, lower your jar that I may drink,’ and who replies, ‘Drink, and I will also water your camels’—let her be the one whom You have decreed for Your servant Yitzchak. Thereby shall I know that You have dealt graciously with my master.
Torah Temimah points to Chullin 95b. E-Daf · Sefaria — Chullin 95b
TT lemma: והיה הנערה.
Rav said: Any divination that is not like that of Eliezer the servant of Avraham is not [forbidden] divination.
Custom (Bavli — definition of prohibited nichush)
The prohibition of nichush applies only when one treats the sign as decisive and acts upon it, as Eliezer did; casual omens that do not govern one’s conduct are not forbidden under that rubric.