Hazrat ‘Aamir bin ‘Abdillah bin Zubair (rahimahullah) reports:

Hazrat Abu Bakr (radhiyallahu ‘anhu) would purchase and free slaves who had accepted Islam in Makkah Mukarramah. In this manner, he would purchase and free the old women and female slaves. Noticing this, his father suggested to him, “O my son! I notice that you are purchasing and freeing the weak slaves! Why do you not purchase and free slaves who are strong men so that they can give you support, protect you and defend you?” Hazrat Abu Bakr (radhiyallahu ‘anhu) replied, “O my father! I am only freeing them for the sake of Allah Ta‘ala (not for my personal benefit).” (Taareekh-ul-Khulafaa pg. 126)

It was on account of Hazrat Abu Bakr (radhiyallahu ‘anhu) using his wealth to purchase and free slaves that were being tortured for accepting Islam that the following verses were revealed:

وَ سَیُجَنَّبُہَا الۡاَتۡقَی ﴿ۙ۱۷﴾ الَّذِیۡ یُؤۡتِیۡ مَالَہٗ یَتَزَکّٰی ﴿ۚ۱۸﴾ وَ مَا لِاَحَدٍ عِنۡدَہٗ مِنۡ نِّعۡمَۃٍ تُجۡزٰۤی ﴿ۙ۱۹﴾ اِلَّا ابۡتِغَآءَ وَجۡہِ رَبِّہِ الۡاَعۡلٰی ﴿ۚ۲۰﴾ وَ لَسَوۡفَ یَرۡضٰی ﴿٪۲۱﴾

And the most God-fearing one (i.e. Hazrat Abu Bakr (radhiyallahu ‘anhu)) will be saved from it (the fire of Jahannum), he who spends his wealth (in charity e.g. through purchasing and freeing slaves) in order to gain purification. There is no favour (that he does to anyone) in exchange of which he expects a recompense (e.g. freeing Hazrat Bilaal (radhiallahu ‘anhu)), except (he does whatever he does) with the intention of earning the pleasure of his Lord, the Most High. And surely he will soon be happy (with the rewards that his Lord will bestow upon him). (Surah Layl v. 17-21)

(Taareekh-ul-Khulafaa pg. 126)

Haafiz Ibnul Jowzi (rahimahullah) has mentioned that there is consensus of the ‘Ulamaa that these verses were revealed in regard to Hazrat Abu Bakr (radhiyallahu ‘anhu).

(Taareekh-ul-Khulafaa pg. 113)