The Book Pertaining to the Merits of the Companions (Allah Be Pleased With Them) of the Holy Prophet (May Peace Be Upon Him) (Kitab Al-Fada'il Al-Sahabah)
Muslim :: Book 31 : Hadith 6009
Anas reported that after the death of Allah's Messenger (may peace be upon him) Abu Bakr said to 'Umar: Let us visit Umm Aiman as Allah's Messenger (may peace be upon him) used to visit her. As we came to her, she wept. They (Abu Bakr and Umar) said to her: What makes you weep? What is in store (in the next world) for Allah's-Messenger (may peace be upon him) is better than (this worldly life). She said: I weep not because I am ignorant of the fact that what is in store for Allah's Messenger (may peace be upon him) (in the next world) is better than (this world), but I weep because the revelation which came from the Heaven has ceased to come. This moved both of them to tears and they began to weep along with her.