Genesis 38:28

And it came to pass when she travailed
Her birth throes came strong and quick upon her: that [the one] put out [his] hand;
which showed that she was like to have a difficult and dangerous time of it; that the birth was not like to be according to the usual and natural order, which may be considered as a correction for her sin: and the midwife took and bound upon his hand a scarlet thread, saying,
this came out first;
she tied this to his wrist, that she might know whose hand it was, and so which was the firstborn; which, to know was a matter of consequence, since to the firstborn there were some special and peculiar privileges.