The Almighty Allah says in the Quran:
"...and be cautious of (your duty to) Allah, by Whom you demand one of another (your rights), and (to) the ties of relationship;"
(Surah Nisa 4:1)
According to Imam al-Baqir (a.s.), the notable point in this verse is that the fear of Allah is mentioned alongwith the fear one should have about breaking relations with kith and kin.
In the book Al Kafi there is a tradition from Imam Ja'far as-Sadiq (a.s.). He says:
"The relatives in this Ayat, include all, and not only the nearest ones. Certainly Allah has ordered kindness towards all the relatives. Allah has given so much importance to this deed that he mentions it with his exalted name."
Kindness to Relatives is Commanded in the Same Way as Namaz and Zakat
It is related from Imam Ali-ar-Reza (a.s.):
"Allah has ordered three things along with three others, in the glorious Quran:
1) Namaz is ordered along with Zakat. If one offers Namaz but does not pay Zakat (when it is due upon him) then his Namaz will not be accepted.
2) Allah has ordered thankfulness to Himself along with the thankfulness to one's parents. If one is not grateful to one's parents it is as if he has not been grateful to Allah.
3) Allah has ordered piety along with kindness to ones kith and kin. Then one who is not kind towards the relatives is not pious."
source : GREATER SINS by Ayatullah-ul-Uzma Sayed Abdul Husain Dastghaib Shirazi (r.a.)
