The Ruling of crying and wailing over a Dead Person

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 ﷺ رفع إليه ابن ابنته وهو في الموت، ففاض عينا رسول الله ﷺ فقال له سعد: ما هذا يا رسول الله؟! قال: "هذه رحمة جعلها الله تعالي في قلوب عباده الرحماء" ((متفق عليه)) .

Anas (May Allah be pleased with him) reported:
The Messenger of Allah ﷺ came to his son Ibrahim (May Allah be pleased with him) when he was breathing his last. The eyes of the Messenger of Allah ﷺ began shedding tears. 'Abdur-Rahman bin 'Auf (May Allah be pleased with him) said, "O Messenger of Allah, you too weep?" He ﷺ said, "O Ibn 'Auf! It is mercy." Then he began to weep and said, "The eyes are shedding tears and the heart is grieved, and we will not say except what pleases our Rubb. O Ibrahim! Indeed we are grieved by your departure."

[Al-Bukhari].

وعن أنس رضي الله عنه أن رسول الله ﷺ دخل علي ابنه إبراهيم رضي الله عنه وهو يجود بنفسه فجعلت عينا رسول الله ﷺ تذرفان . فقال له عبد الرحمن بن عوف: وأنت يا رسول الله ؟! فقال: “يا ابن عوف إنها رحمة” ثم أتبعها بأخرى، فقال:”إن العين تدمع والقلب يحزن ، ولا نقول إلا ما يرضي ربنا، وإنا بفراقك يا إبراهيم لمحزونون". ((رواه البخاري، وروي مسلم بعضه)). والأحاديث في الباب كثيرة في الصحيح مشهورة والله أعلم.