Mishkat al-Masabih 1875 — Zakat

A'isha Narrated from:

When some of the Prophet’s wives asked him which of them would join him soonest, he replied that it would be the one with the longest arm. So they took a rod and measured, and Sauda was the one among them who had the longest arm. They later came to know that sadaqa was the meaning of the length of the arm, for Zainab was the one who joined him soonest and she was fond of giving sadaqa.* Bukhari transmitted it.In Muslim’s version she reported God’s messenger as saying, “The one of you who will join me first is the one who has the longest arm.” She said they measured one another’s arms to see which was the longest, and the one with the longest was Zainab because she worked with her hand and gave sadaqa. * She was called Umm al-masakin (mother of the needy), a title given her in the pre-Islamic period.