Agrippa, being anxious to ascertain the number of the male population of Israel, instructed the priest to take accurate note of the Paschal lambs. On taking account of the kidneys, it was found that there were sixty myriad couples (which indicated) double the number of those that came up out of Egypt, not reckoning those that were ceremonially unclean and those that were out traveling. There was not a Paschal lamb in which less than ten had a share, so that the number represented over six hundred myriads of men.
King Agrippa Counted the People of Israel by Paschal Lambs
Hebraic Literature (1901), Talmud — Pesachim 64b