Sifrei Devarim 301
English: “And the Egyptians dealt ill with us” — as it is said, “Come, let us deal wisely with him, lest he multiply, and it come to pass that when war occurs….”
Custom (scriptural cross-reference / gezerah of narrative).
The declaration’s first clause is not vague; it points to the specific plan of the Egyptians to reduce Israel by calculated affliction.