An excerpt from one of Avicenna’s (in all probability) early works, entitled A treatise on knowledge of the rational soul and its states (ed. N. Nadir, Beirut: 1960), ch. 3, pp. 32-33:
For the soul is of the category of substance and its association (muqarina) with the body is of the category of the relative (al-muzaf). A relation (al-izafa) though is the weakest of accidents; for its existence is not fully realized through its subject but rather depends on something else, which is the thing to which there is a relation (al-izafa ilayhi). And so how can a substance that subsists by itself cease to be by the ceasing to be of the weakest of accidents which depends on it?