The commentary of the word of Allah, the High:
وَإِن تَظَاهَرَا عَلَيْهِ فَإِنَّ اللهَ هُوَ مَوْلاَهُ وَجِبْرِيلُ وَصَالِحُ الْمُؤْمِنِينَ وَالْمَلاَئِكَةُ بَعْدَ ذٰلِكَ ظَهِيرٌ
“…and if you back up each other against him, then surely Allah it is Who is his Guardian, and Jibreel and the good-doer from the believers, and the angels after that are the aides.”
Shaikh al-Tabarsi (r.a.) in Majma’ al-Bayaan writes, “Both Shiite and Sunni traditions have been recorded that the term ‘the good-doer from the believers’ implies Ali (a.s.) and it’s the view of Mujahid. In the book, ‘Shawaahed al-Tanzeel’ vide the chain of narrates ending at Sudair al-Sairafi from Imam Abu Ja’far (a.s.), who said, “Indeed, the Messenger of Allah (s.a.w.a.) introduced Ali to his companions twice: First, when he (s.a.w.a.) declared, ‘Of whosoever I am his master, Ali is his master too.’ Second, when the verse ‘then surely Allah it is Who is his Guardian, and Jibreel and the good-doer from the believers’ was revealed, the Messenger of Allah (s.a.w.a.) took the hand of Ali (a.s.) and said, ‘O people! He is ‘the good-doer from the believers’.” Asmaa Bint Umays said, ‘I heard the Holy Prophet (s.a.w.a.) say, ‘And ‘the good-doer from the believers’ is Ali Ibn Abi Taalib (a.s.).’”
In Ghaayah al-Maraam, six traditions from Sunni sources have been mentioned.  Some of these are as follows:
Ibn Shahr Aashob has recorded in his book al-Manaaqeb from Sunni references vide Tafseer Abu Yusuf Yaqub Ibn Sufyaan al-Niswi, al-Kalbi, Mujahid, Abu Saaleh and al-Maghrebi from Ibn Abbas, “Hafsah saw the Holy Prophet (s.a.w.a.) with (his wife) Maariyah al-Qibtiyyah in the house of Ayeshah. He (s.a.w.a.) said to Hafsah, ‘Will you conceal my secret?’ She replied in the affirmative. He (s.a.w.a.) confided, ‘I have made her (Maariyah) unlawful for myself due to the purity of her heart.’ Hafsah informed Ayeshah and revealed unto her about the prohibition of Maariyah. Ayeshah spoke to the Holy Prophet (s.a.w.a.) about the matter and the verse “And when the Prophet secretly communicated a piece of information to one of his wives…. then surely Allah it is Who is his Guardian, and Jibreel and the good-doer from the believers”. He said, ‘By Allah! The good-doer from the believers is Ali (a.s.). He says Allah is sufficient for him and the angels after that are the aides.’
Al-Bukhari and al-Mosuli record that Ibn Abbas said, “I asked Umar Ibn al-Khattaab about the two women who were backing each other against the Prophet (s.a.w.a.), he replied, ‘Hafsah and Ayeshah’.”
As for the traditions from our sources, then they are truly copious. Some of which are as follows:
1) In Ghaayah al-Maraam from Muhammad Ibn Maahiyaar – a reliable person – in his exegesis while discussing the verses that were revealed in the glory of the Ahle Bait (a.s.) has brought fifty-two (52) traditions under this verse from both Shia and Sunni sources.
2) Narrated unto us Ja’far Ibn Muhammad al-Husaini from Eesa Ibn Mehraan from Mukhaawel Ibn Ibraheem from Abd al-Rahmaan al-Aswad from Muhammad Ibn Abdullah Ibn Abi Raafe’ from Fatemah (s.a.), who said, “The day when the Messenger of Allah (s.a.w.a.) expired, he (s.a.w.a.) became unconscious and then regained consciousness while I was crying, kissing his hands and saying, ‘Who is there for me and my children after you, O Messenger of Allah?’ He (s.a.w.a.) said, ‘After me, there is Allah for you and my successor, the good-doer from the believers, Ali Ibn Abi Taalib (a.s.).”
I say: Traditions that prove this verse to be revealed in the glory of our master Ameerul Momineen (a.s.) and that the good-doer from the believers refers to him (a.s.) support what has been established by the consecutive traditions from both the sects. In fact, it necessarily establishes our master Ameerul Momineen (a.s.) is the most superior of the believers, their leader and the best of them after the Holy Prophet (s.a.w.a.). He (a.s.) was the most helpful towards Allah – the High – and the Messenger of Allah (s.a.w.a.) in all instances. Hence, the distinction of being a good-doer, righteous and helpful will not be proper for anyone among the believers except him (a.s.). Moreover, distinction is not proper in any field except for the one who is not the best in the presence of the best. When it has become clear for you that he (a.s.) is distinct in righteousness and help for the Messenger of Allah (s.a.w.a.) from amongst all the believers because his (a.s.) righteousness was perfect and his (a.s.) help perfect, the distinction of Caliphate and Imamate for him (a.s.) becomes apparent. Since, evidently it is impossible for the one who is most special in front of Allah and the Messenger of Allah (s.a.w.a.) should follow and be under the mastership of the one who does not enjoy such a position in front of Him – the High.
Do you think that it is permissible that the one who is not the most distinct to be the followed one and master of the one whom Allah has made distinct with righteousness and assistance for His Messenger (s.a.w.a.) from amongst all the believers and associated his assistance for His Messenger (s.a.w.a.) as His Own assistance and the assistance of the trustworthy Jibraeel (a.s.)?
All Praise is for Allah Who guided us to this and it would not have been possible for us to be guided had Allah not guided us.