First of all I must thanx to scorpIIon for according an opportunity to elaborate this topic/issue.
If any of religious scholar declare it as permissable, then it goes against not only to the traditions of Masumeen(a.s) but also to the Verses of Quran. And Biradar-e-Azeez like all other true Shias I too follow only the Quran and Traditions of Masumeen(a.s.) as we see the prophet has choosed for us only two source of guidance:
"I'm leaving amongst you two most valuable things- one is Allah's book and the other is my Progeny (Itrat, Ahlebait). These two never separates from each other. Such that they will meet me at the fountain of Kousar (Houz-e-Kausar). Whoever binds himself to these two will definitely attain salvation and whoever distances himself from these two will definitely be ruined. Till you are bounded with these two you will never ever go astray".
Hence to be safe from going astray and being disgraced, it is essential to practice on Quran and Ahlebait (AS). Neither by saying 'Hasbona Kitaballah' (only Quran is sufficient) can leave Ahlebait (AS) nor can add Intellect (Aql) and Ijma (Consensus) to these two. It doesnot means that I disobey or rejects the religious scholars, but I never follow their personal opinion, the order he passes should be in the light of Verse of Quran or Tradition of Masumeen(a.s.). If I found an order of even Hz. Salman (ra) the top ranked, which contradict with the tradition of Masumeen(a.s.) then I reject the order of Hz. Salman(ra). So now let us come to the topic of "Marriage of a Shia Girl with Non Shia". First we will see who are superior, a shia ? or a non shia ? No doubt in it that, A person who testify that "there is no god but Allah" is superior than who deny this, then a person who also testify that "Mohammed(s) is prophet to Allah" is superior to the person who submit only one testimony and who submit more than two testimonies are more superior than who submit only two testimonies. Please see Sura-e-Muarij Verses 33 to 35 " And those who are upright in their testimonies ( Shahadaatehum ), And those who keep a guard on their prayer, Those shall be in gardens, honored" It is important to note here that the word Shahad’aat ( Plural ) in Arabic is only used for atleast 3 testimonies - It cannot be used for 2 testimonies , For 2 testimonies the word in Arabic is ‘ Shahadatain ‘ In the above Ayat-e-Quran God Almighty is describing the glories of people who testifies 3 Shahad’aat in their Namaz and safeguards their prayers ( Namaz ). And also Allah says: "Those who believe and do righteous deeds are the best of the creatures. Their reward from their Lord shall be everlasting gardens, below which flow rivers, they will abide there forever. Well pleased is God with them and they are well pleased with Him. The Holy Qur'an 98:7 Numerous recognised Sunni scholars have in their commentaries recorded that following the descent of this verse the Prophet (s) declared: "I swear by the one who controls my life that this man (Ali) and his Shi'a shall secure deliverance on the day of resurrection". Tafsir Ibne Jarir, Volume 33 page 146 (Cairo edition) narrated from Hadhrath Muhammad bin Ali (as); Tafsir Durre Manthur by Jalaladeen Suyuti, Volume 6 page 379 -3 separate chains; Tafsir Fatha ul bayan Volume 10 page 333 (Egypt edition). So I think it is clear that Shias' are superior than anybody. No we will see what is mean by "Kuff" and to whom it is applicable. "Kuff" = suitable pair, and it is applicable to a girl only. What is suitable pair ? Suitable pair as per the History of Islam and practice of Masumeen(a.s.: A person who is either higher ranked or atleast same ranked, person below the rank has been never treated as Kuff. And now we will see what are the opinions of Masumeen(a.s.) in this regard: We see in Furooh – e – Kafi volume 5, Bihar – Al – Anwar, Ad – Damatus – Sakiba by Agha Baqar Dahdashti Bahbani Najfi (ra) Volume 2, page 544 Urdu and Rasoom – Ush – Sharayya Fi Mizan Asharayya by Mohammed Hasnain Sabqi Najfi (ra) etc. This is quoted here-under for final analysis. Imam As -Sadiq (as) was approached by a Khawarij and asked the hand of Syedani and Imam (as) replied:-
“Your ‘‘kufv’ is in your own blood, your own ‘Hasab’ and your own people (Qoum - قوم
and positively Allah (swt) has kept Sadaqah away from us which is the dirt of the hands of people (in general) and we hate/dislike to include in that superiority/virtue given to us by Allah (swt), someone for whom Allah (swt) has not given the virtue/superiority that he has laid down for usâ€. And also there is clear instructions from the same Imam(as) that "MOMINA KA KUFF SIRF MOMIN HAI". So I think now you may convince, and if you want more referneces on this topic, Insha-allah wa Insha-Ali(a.s.) I will try my level best to provide. Please remember me in your prayers. Bye.