Reference for Beitzah 8:8

רב אסי ספוקי מספקא ליה ועביד הכא לחומרא והכא לחומרא

Rav Asi was extremely doubtful [whether it is one holiness or two] and [therefore] was stringent here [in the case of havdallah] and stringent here [in the case of the egg].

Jastrow