Sahih Bukhari Volume 2, Book 24, Hadith 1421

حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ فِرَاسٍ، عَنِ الشَّعْبِيِّ، عَنْ مَسْرُوقٍ، عَنْ عَائِشَةَ، رضى الله عنها أَنَّ بَعْضَ، أَزْوَاجِ النَّبِيِّ صلى الله عليه وسلم قُلْنَ لِلنَّبِيِّ صلى الله عليه وسلم أَيُّنَا أَسْرَعُ بِكَ لُحُوقًا قَالَ ‏"‏ أَطْوَلُكُنَّ يَدًا ‏"‏‏.‏ فَأَخَذُوا قَصَبَةً يَذْرَعُونَهَا، فَكَانَتْ سَوْدَةُ أَطْوَلَهُنَّ يَدًا، فَعَلِمْنَا بَعْدُ أَنَّمَا كَانَتْ طُولَ يَدِهَا الصَّدَقَةُ، وَكَانَتْ أَسْرَعَنَا لُحُوقًا بِهِ وَكَانَتْ تُحِبُّ الصَّدَقَةَ‏

Narrated By 'Aisha : Some of the wives of the Prophet 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 and she used to love to practice charity. (Sauda died later in the caliphate of Muawiya).