Which daughter of the Prophet (sallallahu ‘alayhi wasallam) does the following Hadith refer to and why did he refuse to go in the first instance?
Usama (radiyallahu ‘anhu) said: ‘Once, one of the daughters of the Prophet (sallallahu ‘alayhi wasallam) sent a message to him while we were with him. In the message she wrote, ‘My child is going to die; please come.’ Allah’s Messenger (sallallahu ‘alayhi wasallam) sent his reply saying, ‘Whatever Allah takes is for Him and whatever He gives is for Him, and everything with Him has a limited time in this world. Therefore, you should be patient and hope for Allah’s reward.’
Then again, she sent for him, so the Prophet (sallallahu ‘alayhi wasallam) went to see her, and we accompanied him. When we got there, the sick child was brought to him and he took him on his lap, while the child was having difficult breathing. Seeing this, Allah’s Messenger (sallallahu ‘alayhi wasallam) started to cry. At this sight Sa’d expressed, ‘What is this, O Allah’s Messenger (sallallahu ‘alayhi wasallam)? The Prophet (sallallahu ‘alayhi wasallam) replied, ‘This is the mercy which Allah has put in the hearts of whoever He wants of His slaves, and verily Allah is merciful only to those of His slaves who are merciful to others.’’
(Sahih Bukhari, Hadith: 1284, 5655, 6655, 7377, 7488, and Al-Adabul Mufrad, Hadith: 512)
The Muhaddithun have differed with regards to which daughter of Nabi (sallallahu ‘alayhi wasallam) was referred to in this particular Hadith. Nonetheless, many of them have given preference to the opinion that it was Sayyidah Zaynab (radiyallahu ‘anha). Amongst them were ‘Allamahs: Ibn Hajar Al-‘Asqalani, ‘Ayni, Qastallani, Suyuti, Zakariyya Al-Ansari, Ibn Hajar Al-Haytami, Mulla ‘Ali Qari, and others (rahimahumullah).
(Fathul Bari, Hadith: 1284, ‘Umdatul Qari, Hadith: 1284, Irshadus Sari, Hadith: 1284, At-Tawshih, Hadith: 1284, Minhatul Bari, Hadith: 1284, Fathul Ilah, Hadith: 1723, Mirqat, Hadith: 1723)
A few other ‘Ulama and Muhaddithun felt that a different daughter of Nabi (sallallahu ‘alayhi wasallam) was being referred to in the Hadith. ‘Allamah Birmawi (rahimahullah) has mentioned that it is very possible many incidents of the same nature befell multiple daughters at different times.
(Irshadus Sari, Hadith: 1284; Also see Fathul Ilah, Hadith: 1723 and Shaykh Muhammad Zakariyya Al-Kandehlawi’s footnotes on Badhlul Majhud, Hadith: 3125)
The commentators of Hadith have mentioned a variety of different possible reasons for which Nabi (sallallahu ‘alayhi wasallam) did not comply to the wishes of his daughter at first. A few of these reasons are mentioned below:
It is possible Nabi (sallallahu ‘alayhi wasallam) wanted to initially express a heightened sense of submission to Allah Ta’ala [thereby expressing his humility and acceptance to the decree of his Rabb], and to teach this level of submission to his daughter (radiyallahu’anhua).
Nabi (sallallahu ‘alayhi wasallam) could have been preoccupied with something of greater importance when the message first reached him, therefore he wasn’t able to immediately comply to the wish of his daughter.
Some commentators have mentioned that it is possible that Nabi (sallallahu ‘alayhi wasallam) initially refrained from honoring the request of his daughter to demonstrate and explain to the Ummah [the Muslims, both present and future] that it is not mandatory or binding upon a person to honor such invitations, unlike the Walimah for example [as honoring an invitation to a Walimah, is considered to be an extremely emphasized Sunnah, provided there is nothing preventing one from doing so].
(Ikmalu Ikmalil Mu’lim, Hadith: 924, Fathul Bari, Hadith: 1284 and ‘Umdatul Qari, Hadith: 1284)
And Allah Ta’ala knows best.