Is it ensure, insure, or assure?
An event beyond human control — e.g., hurricane, earthquake, volcanic eruption (see volcano), etc. — for which there is no legal redress. The phrase is frequently used by insurance companies and lawyers.
Note: As a legal term relating to property damage, it appears in insurance contracts: “After the flood, Papovich was dismayed to discover that his house was not insured against acts of God.”