Exodus 1:14
And they made their lives bitter with hard bondage, in mortar, and in brick, and in all manner of service in the field: all their service, wherein they made them serve, was with rigor.
Exodus 12:8
And they shall eat the flesh in that night, roast with fire, and unleavened bread; and with bitter herbs they shall eat it.
Exodus 15:23
And when they came to Marah, they could not drink of the waters of Marah, for they were bitter: therefore the name of it was called Marah.