Riyad as-Salihin 926
Usamah bin Zaid (May Allah be pleased with him) reported:
A grandson (child of the daughter) of the Messenger of Allah (ﷺ) was presented to him while the child was at his last breath. Tears began to flow from the eyes of the Messenger of Allah (ﷺ). Sa'd said to him: "What is this, O Messenger of Allah?" He (ﷺ) said, "It is mercy which Allah has placed in the hearts of his salves. Allah bestows His Mercy on the merciful among His slaves." [Al-Bukhari and Muslim] .
وعن أسامة بن زيد رضي الله عنهما أن رسول الله صلى  الله عليه وسلم  رفع إليه ابن ابنته وهو في الموت، ففاض عينا رسول الله صلى  الله عليه وسلم  فقال له سعد‏:‏ ما هذا يا رسول الله‏؟‏‏!‏ قال‏:‏ ‏
"‏هذه رحمة جعلها الله تعالي في قلوب عباده الرحماء‏"‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏ ‏.‏