Halakhah do Rodzaju 13:16

4. Rashi, I Chronicles 27:24, seemingly ignoring the sources cited in both Berakhot 62b and Yoma 22b, posits two entirely different verses as sources for this prohibition. The passages "If a man can number the dust of the earth, then shall your seed also be numbered" (Genesis 13:16) and " 'Look now toward heaven and count the stars if you are able to count them'; and he said unto him, 'So shall your seed be' " (Genesis 15:5) are interpreted by Rashi, not simply as blessings, but as prohibitions against counting the progency of Abraham. In his commentary on I Samuel 15:4, Rashi cites yet a third verse, "I will surely do you good and make your seed as the sand of the sea which cannot be numbered for multitude" (Genesis 32:13) which he renders as "which shall not be numbered for multitide.⁹Cf., Meshekh Ḥokhmah, Parshat Naso, s.v. be-haftorah.