Musnad Ahmad 941:57

Abu Mu'awiyah narrated to us, 'Asim narrated to us, Abu 'Uthman al-Nahdi narrated to me, from Usamah ibn Zayd, who said: Umamah bint Zaynab was brought to the Messenger of Allah, may Allah bless him and grant him peace, while her soul was rattling as if she were in a water skin. He said: "To Allah belongs what He took, and to Allah belongs what He gave, and everything has a specified term." He said: Then his eyes shed tears. Sa'd ibn 'Ubadah said to him: "O Messenger of Allah, do you weep? Did you not forbid weeping?" The Messenger of Allah, may Allah bless him and grant him peace, said: "It is only a mercy that Allah has placed in the hearts of His servants, and Allah only shows mercy to the merciful among His servants."