Narrated `Aisha (RA): Some of the wives of the Prophet (peace be upon him) asked him, “Who amongst us will be the first to follow you (i.e. die after you)?” He said, “Whoever has the longest hand.” So they started measuring their hands with a stick and Sauda’s hand turned out to be the longest. (When Zainab bint Jahsh died first of all in the caliphate of `Umar), we came to know that the long hand was a symbol of practicing charity, so she was the first to follow the Prophet (peace be upon him) and she used to love to practice charity. (Sauda died later in the caliphate of Muawiya).
Sahih al-Bukhari, Vol. 2, Book 24, Hadith 24