BT Suk 26b(8) :דסוסיא שתין נשמי‏ : for a horse (a brief nap) is sixty respirations
See the entire entry for nəšem, nešmā n.m. breathing

BT Suk 26b(8) :דדוד כי דסוסיא דסוסיא שתין נשמי‏ : David's (nap) was like that of a horse, (and the length of a nap) of a horse is sixty breaths
See the entire entry for sūsē, sūsyā n.m. horse