Substance (jawhar) denotes an underlying or subsisting reality, while accident (ʿaraḍ) denotes a quality or state existing in a subject. Body (jism) denotes something extended in spatial directions. The details of these terms differ between theologians and philosophical schools.
For illustration, a wooden board is a body; being warm or cold is a state. Warmth should not be imagined as a second independent wooden board. Yet this illustration alone does not establish a complete theory of indivisible atoms or prime matter.
Distinguishing the terms prepares the question: can the underlying substrate, the body's form, or their combination be beginningless?