love for Household as the prophets\' message requital
When the Qur' an relates what the previous prophets have said, it points out that they have all said: "we do not ask a wage from people, our only reward is from God." However it addresses the Seal of the Prophets thus:
Say: "I do not ask of you a wage for this, except love for (my) relatives." (ash-Shura, 42:23 )
Here there is a need to ask why the rest of the prophets looked for no wage but the most ~noble Prophet~asked for one for his message; why did he want friendship for his near relatives as a requital for his message?
The Qur'an itself provides an answer to this question:
Say: "I have asked no wage of you; that shall be yours. My wage falls only upon God. " (Saba', 34:47)
That is to say, that which I ask for as a wage accrues to you, not to me; this friendship is a halter for your own perfection and reformation, and it is called a wage. Otherwise it is in fact another good which I recommend to you from the point of view that the Household and relatives of the Prophet are people who do not gather round defilement, and whose hems are clean and pure. Love and devotion to these people brings no other result apart from obedience to the truth and adherence to virtues, and it is friendship for them which transmutes and perfects like the elixir.
Whatever the meaning of "~relatives~" may be, it is certain that the most obvious person to whom it is applicable is 'Ali. ~Imam Fakhru'd-Din ar-Razi~ says:
"~Zamakhshari~ relates in his (Qur'anic exegesis) ~al-Kashshaf~: `When this verse was sent down they said: "O Messenger of Allah! Who are the relatives to whom our love is due?" He said: " `~Ali~ and ~Fatimah~ and their sons."
"It is thus established from this tradition that these four persons are "relatives" of the Prophet, and that they should enjoy the respect and love of the people, and this matter can be reasoned out in a number of ways:
" 1 - The verse: except love for my relatives.
" 2 - There is no doubt that the Prophet dearly loved Fatimah, and he said: `Fatimah is a part of my body; what harms her harms me.' he also loved 'Ali and the Hasanayn (Hasan and Husayn), since a great number of mutawatir traditions (those which are narrated by so many as to make doubt impossible) have reached us on this subject. Thus friendship of them is obligatory on all the community (The love of the Prophet towards them had no personal aspect, that is, it was not only because, for example, they were his children and grandchildren and if someone else had been in their place he would have loved them. The Prophet loved them because they were exemplary persons and God loved them, for the Prophet had other children whom he did not love to this extent and to whom his community had no such obligation), because the Qur'an commands: And follow him (the Prophet), haply you will be guided. (al-A'raf, 7:158) "It also commands: You have a good example in Allah's Messenger(al-Ahzab, 33:21). "These (considerations) prove that love for the Family of Muhammad - who are `Ali, Fatimah and the Hasanayn -is obligatory on all Muslims. " [at- Tafsiru 'l-kabir, vo1.27, p.166 -Egyptian ed].
Sources :
attraction and repulsion of Imam Ali p.b.u.h- pages: 88to90