‘Aa’ishah narrated that the Messenger of Allah, sallallaahu ‘alayhi wa sallam, said: “The fastest amongst you in joining me [in Paradise] is the one who has the longest arm [spends more in charity].” ‘Aa’ishah added, “So we used to stretch our arms to see who has the longest arm, and it was Sawdah. But the one amongst us (who truly had) the longest arm was Zaynab because she used to do things with her hand (and sell it) and then spend its price in charity.”
An-Nawawi said: “In the beginning they thought that the Prophet of Allah, sallallaahu ‘alayhi wa sallam, was referring to the actual arm’s length, and that is why they used to measure their arms in length, and Sawdah had the longest arm. On the other hand, Zaynab was the most generous of all, and when she died (she was the first to die after the death of the Prophet of Allah, sallallaahu ‘alayhi wa sallam) they realized that it was a metaphor and that the Prophet of Allah, sallallaahu ‘alayhi wa sallam, meant by that the one who spent more in charity and is more generous.”
Ibn Hajar said: “This narration is evidence that one should spend as much as he can in charity while he is able to, and that this would be a means for him to join the Prophet of Allah, sallallaahu ‘alayhi wa sallam, in paradise which is the ultimate virtue one can achieve.”