Who are right? Sunni or Shia (Shiite)

Is there a Quranic reason to prove that Shiite (Shia) is the true sect of Islam or Sunni?

Of-course! there are several verses in Quran which can be used to prove Shia are right or Sunnah (Sunni).

The main difference between Shia and Sunni is the subject of Imamat; Shia says Imam is chosen by Allah and He must say to his prophet who is the Imam after him. They say that the prophet Muhammad assigned Ali (as) as his Imam. On the other hand Sunni brothers say that Imam must be chosen by a council and Abubakr is the Imam after the prophet. Here I prove that Imam must be chosen by Allah not a council.

Who must choose Imam (Caliphs) of the prophet Muhammad (sawa)?

Imamat in Quran

Quran says :
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Indeed, I will make you an Imam for the people." [Abraham] said, "And of my descendants?" [Allah] said, "My covenant does not include the wrongdoers (Quran 2:124)
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In another place, in Shora chapter, Quran says:
And their affair is [determined by] consultation among themselves (Quran 42:38)
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Sunni Muslims use this last verse and claim that Imamat is an affair of Muslims and they must select an Imam by consultation. However the first verse says that Imamat is not an affair of people, its an affair and covenant of Allah and He must assign the Imam.

So, Imamat (leadership) is covenant of Allah not affair of people, and Imam must be chosen by Allah, not by consultation .

More images about Shia Islam: Shia Truth
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قَالَ إِنِّي جَاعِلُكَ لِلنَّاسِ إِمَامًا قَالَ وَمِن ذُرِّيَّتِي قَالَ لَا يَنَالُ عَهْـــدِي الظَّالِمِينَ (بقره 124) ➕
وَأَمْرُهُمْ شُورَى بَيْنَهُمْ (شوری 38) ✅
الامامةُ هیَ عَهدُ اللّه، ولا امرُ النّاس فَلیسَ فیها شُورَى
في النهاية: ابابکر و عثمان جعلا امام الناس بالشوری و عمر جعل بأمر ابي بکر! ... فلا تقولوا حسبنا کتاب الله ايها المسلمون 

Condolence on Demise of The Prophet Muhammad

Today is Safar 28, the day in where the prophet Muhammad (sawa) passed away:

In the beginning of 11 AH, the Prophet (s) became sick and passed away. Before he passed away, when he was very ill, he gave a farewell speech to the Muslims and advised them to be kind to one other. He also said "If I owe anything to anyone, they should come to me to ask for it or else, they should disregard it. If I have annoyed anyone, I am ready to be punished in retaliation for it"^[70].

The Prophet (s) passed away on the 28th of Safar or on the 12th of Rabi' al-Awwal 11 AH at the age of 63. It is mentioned in Nahj al-balagha that at the time of his death, the Prophet's (s) head lay on the chest of Ali (a).^[71]

At the time of his death, none of his children were alive except for Fatima (a). All of his other children had passed away, including Ibrahim, who was born one or two years before the Prophet's (s) death. Ali (a), with the help of some others, as per the Islamic tradition, washed the Prophet's (s) body, and shrouded and buried him in his house, where it is now located in Masjid al-Nabi. 

Condolences on death (or martyrdom) of the Prophet (SAWA) and Martyrdom of Imam Hassan (AS) and Imam Reza (AS).

In 28th of Safar 632 (11AH Islamic Calendar) the prophet Muhammad (SAWA) was dead. In the same day at 50 AH his grandson Imam Hassan was martyred by poison.

In 30th of Safar 203 AH, Imam Reza (AS), the 8th Imam of Shia Muslims was martyred by Mamun, Caliph of Bani Abbas. Imam Reza was martyred by poisonous grapes

What happened after the death of the Prophet?

How was Abubakr selected as the successor of the Prophet?

While Ali b. Abi Talib (a) and the Banu Hashim were washing the corpse of the Prophet (s) as per Islamic tradition, a few influential Muslims decided to choose the next leader for the ummah-- disregarding what the Prophet (s) had said just two months prior to his demise (see: Ghadir Khum). A number of people from Mecca (the Muhajirin) and Medina (the Ansar) gathered in a place called Saqifa Banu Sa'ida. They wanted a ruler to be chosen for the Muslims as soon as possible.  Finally they choose AbuBakr despite of the Prophet emphasis on leadership of Ali (as) after him several times during his life (See: Hadith Ghadeer, Hadith Manzilat, Hadith AlThaqalayn, Hadith Yawm al Inzar).
 

The holy shrine of the Prophet Muhammad (SAWA) in Madina

Grave of Imam Hassan (AS) in Baqi'. The holy shrine was destroyed by Al-e-Saud, about 100 years ago

The holy shrine of Imam Reza (AS) in Mashhad, Iran