All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Islam has legislated marriage among members of different families and clans to enlarge the scope of social ties in line with the following verse: " and made you into nations and tribes, that ye may know each other (not that ye may despise (each other)"{Al-Hujurat/13}.
Thus, lineage is a means of knowing each other.
Islamic Sharia recommends selecting a pious wife, and disregards other factors since the Prophet (PBUH) said in this regard, "A woman is married for four things, i.e., her wealth, her family status, her beauty and her religion. So you should marry the religious woman (otherwise) you will be a losers." [Related by Al-Bukhary].
Values their partners as far as considerations of lineage and piety are concerned, whether from their clan or not, in accordance with the saying of the Prophet(PBUH): "When someone whose religion and character you are pleased with comes to you then marry (her to) him"{Abu-Dawud}. Accordingly, if it is in the best interest of the man or the woman to marry someone from a different clan, then this is better.
In addition, Islamic Sharia forbids severing kinship ties with a relative because he has given his daughter or sister in marriage to someone from a different clan since Allah, The Almighty, says in this regard: "Serve God, and join not any partners with Him; and do good- to parents, kinsfolk, orphans, those in need, neighbours who are near, neighbours who are strangers, the companion by your side, the wayfarer (ye meet), and what your right hands possess: For God loveth not the arrogant, the vainglorious"{An-Nisa`/36}.
And the Prophet(PBUH) said: "Do not harbour grudge against one another, nor jealousy, nor enmity; and do not show your backs to one another; and become as fellow brothers and slaves of Allah. It is not lawful for a Muslim to avoid speaking with his brother beyond three days."{Agreed upon}. And Allah knows best.