Parashas Eikev · Passuk 9:17
Thereupon I gripped the two tablets and flung them away with both my hands, smashing them before your eyes.
Torah Temimah points to Pesachim 87b.
TT lemma: ואשברם לעיניכם (unit 3 of 3).
English: R’ Alexandri said: The writing of the tablets returned to their source, as it is written, “I smashed them before your eyes.” And it was taught: The tablets were broken and the letters flew away.
Custom (letters flew when the tablets broke)
When the tablets shattered, the engraved letters departed; the breakage was visible, the script not left as ordinary debris.