الاستصحاب
al-Istiṣḥāb
Presumption of continuity: an established ruling or state remains in force until evidence shows that it has changed.
What it means
Istiṣḥāb means keeping something as a companion, and in the law it is the principle that an established rule or condition is presumed to continue unless proof shows that it was revoked or has altered. The default is continuity. Faruqi defines it as the continuation of an established law that is not known to have been revoked or rescinded by any later evidence.
Jurists express the principle in the well-known rule that certainty is not removed by doubt, and they draw support from a hadith in which a man felt something during prayer, and the Prophet (peace be upon him) told him not to leave unless he heard a sound or smelled an odour (Sahih al-Bukhari, Sahih Muslim). Jurists agree on its use in practice, but they differ on how much weight it has as a source.
Term and Arabic as listed in Ismail al Faruqi, Toward Islamic English (International Institute of Islamic Thought, 1995), p. 53, listed as AL ISTIṢḤĀB. The definition is restated here.