The interpreters said that this verse was revealed because of Abo Bakr Ass-Siddiq (May Allah be pleased with him), as an example of who are the best, since Abo Bakr (May Allah be pleased with him) gave all his money for the benefit of the Muslims, the first giving was freeing of Saydina Bilal Ibn Rabah (May Allah be pleased with him) who used to be tortured badly before saydna Abo Bakr bought him.