سنن ابن ماجه

It was narrated from ‘Abdullah that the Messenger of Allah (ﷺ) said: “Whoever sends fourth three of his children who had not reached the age of puberty, they will be a strong fortification for him against the Fire.” Abu Dharr said: “I sent forth two.” He said: “And two” Ubayy bin Ka’b, the chief of the reciters, said: “I sent forth one.” He said: “Even one.”