Verš 92:18

jenž ze jmění svého dával,aby čistým se stal,

Tafsir al-Jalalayn

he who gives his wealth to purify himself, offering it as a [means of self] purification before God, exalted be He, by making this payment for the sake of God, exalted be He, and not for show or the sake of reputation, so that he [or the offering] stands purified in the sight of God. This [verse] was revealed regarding the truthful one (al-siddīq) [Abū Bakr], may God be pleased with him, when he purchased Bilāl [the Ethiopian], who was being tortured on account of his faith, and then freed him, whereat the disbelievers said, ‘He only did this in return for a favour which he [must have] owed him’, and so the following was revealed: