If you read the article it outlines what international law says:

Even if Israel succeeds in proving Shifa conceals a Hamas command center, the tenets of international law remain in place, said Jessica Wolfendale, expert in military ethics at Case Western Reserve University in Ohio.

“It doesn’t license an instant attack,” she said. “Steps need to be taken to protect the innocent as much as possible.”

If the harm to civilians is disproportionate to the military objective, the attack is illegal under international law.

They need to not only provide proof beforehand but also take steps to mitigate innocent death and injury.