Because Allah the Exalted has said in Surah At-Tahrim: "Save yourselves and your families from a Fire"—that is, forbid them from evil deeds. And the Prophet (peace and blessings of Allah be upon him) said: "Each of you is a shepherd and each of you will be questioned about his flock." And if this weeping and wailing is not a custom of his family, and then suddenly someone starts weeping over him, then Aisha (may Allah be pleased with her) taking evidence from this verse is correct: "No bearer of burdens shall bear the burden of another. And if a soul laden with burden calls another to carry its load, nothing of it will be carried, even if he be a near relative." And weeping without wailing or beating oneself is permissible. And the Prophet (peace and blessings of Allah be upon him) said: "Whenever any innocent blood is shed in the world, some of its burden falls upon the first son of Adam, Qabil, because he was the first to establish the practice of unjust killing."

Narrated Usama bin Zaid: The daughter of the Prophet (p.b.u.h) sent (a messenger) to the Prophet requesting him to come as her child was dying (or was gasping), but the Prophet returned the messenger and told him to convey his greeting to her and say: "Whatever Allah takes is for Him and whatever He gives, is for Him, and everything with Him has a limited fixed term (in this world) and so she should be patient and hope for Allah's reward." She again sent for him, swearing that he should come. The Prophet got up, and so did Sa`d bin 'Ubada, Mu`adh bin Jabal, Ubai bin Ka`b, Zaid bin Thabit and some other men. The child was brought to Allah's Apostle while his breath was disturbed in his chest (the sub-narrator thinks that Usama added:) as if it was a leather water-skin. On that the eyes of the Prophet (p.b.u.h) started shedding tears. Sa`d said, "O Allah's Apostle! What is this?" He replied, "It is mercy which Allah has lodged in the hearts of His slaves, and Allah is merciful only to those of His slaves who are merciful (to others).