The Purified Imams (a.s.) are the Hablul Mateen (strong rope) and Urwatul Wuthqa (firmest handle)
And there are many Quranic verses on this topic.
فَمَنْ يَكْفُرْ بِالطَّاغُوتِ وَيُؤْمِنْ بِاللَّهِ فَقَدْ اسْتَمْسَكَ بِالْعُرْوَةِ الْوُثْقَى لَا انفِصَامَ لَهَا وَاللَّهُ سَمِيعٌ عَلِيمٌ.
…whoever disbelieves in the Shaitan and believes in Allah he indeed has laid hold on the firmest handle, which shall not break off, and Allah is Hearing, Knowing. (Surah Baqarah 2:256)
We should know that the Shaitans are all (false) deities other than Allah. In many traditions Imam (a.s.) has compared the false deities to the unjust rulers and enemies of religion whether they be Jibt, Tagut or Uzza and also considered the two hypocrites, the first and the second (caliphs) one as the Sanam (idols) of Quraysh. (And it is narrated from Imam Sadiq (a.s.) that in the book of Allah our enemies are called ‘Fahsha’, ‘Munkir’, ‘Avsan’, ‘Jibt’ and ‘Taghut’.
Kulaini has narrated from Imam Sadiq (a.s.) that ‘Urwatul Wuthqa’ refers to the faithful man. And in another tradition he says that ‘Urwatul Wuthqa’ is to bring faith on only one God, Who has no partner.
There is a tradition in Mahasin by the same Imam that ‘Urwatul Wuthqa’ means monotheism and Ibne Shahr Aashob has narrated from Imam Baqir (a.s.) that ‘Urwatul Wuthqa’ is the love of we Ahlul Bayt (a.s.) and in Uyoon Akhbar Ridha there is a tradition from the same Hazrat that the Holy Prophet (S) said that those who want to board the ship of salvation and get attached to ‘Urwatul Wuthqa’ and ‘Hablul matin’ hold of Allah, should after me befriend Ali and be inimical to his enemies and follow the Imams from his progeny.
Also from the same Hazrat it is narrated that the Holy Prophet (S) said that those who want to hold ‘Urwatul Wuthqa’, should love Ali and my Ahlul Bayt.
Also there is a tradition that the Holy Prophet (S) said: Those who follow the Imams from the progeny of Imam Husain (a.s.) then without any doubt they have followed Allah and those who disobey them are those who have disobeyed Allah. They are ‘Urwatul Wuthqa’ and they are Wasilah (medium) for the people to reach Allah.
According to another tradition Imam Ridha (a.s.) wrote to Mamoon about Islam, Shariah and religion. It was also written that the earth is never without the Hujjat (proof) of Allah. And they are ‘Urwatul Wuthqa’ and Imams of guidance and proof of Allah on the people.
There is a tradition in Tawheed that Amirul Momineen (a.s.) said that I am ‘Hablullah-al-Matin’ and I am ‘Urwatul Wuthqa’.
There is a tradition in Kamaluddeen that Imam Ridha (a.s.) said: We are the Hujjat (proof) of Allah on the people and we are the ‘words of piety’ and ‘Urwatul Wuthqa’.
In Maniul Akhbar there is a tradition from the Holy Prophet (S) that those who want to get attached to the ‘Urwatul Wuthqa’ which shall never break, should attach themselves to my brother and my vicegerent, Ali Ibne Abi Talib’s Wilayat. Without any doubt he will not be destroyed that befriends him and has belief in his Imamate. And he will not get salvation that regards him as an enemy.
In Tawilul Aayaat there is a tradition from Imam Ridha (a.s.) that the Holy Prophet (S) said that those who want to catch hold of the ‘Urwatul Wuthqa’, should be attached to the Wilayat of Ali Ibne Abi Talib.
According to another tradition from Zaid Ibne Ali it is the true and intense love for Aale Muhammad (a.s).
وَاعْتَصِمُوا بِحَبْلِ اللَّهِ جَمِيعًا وَلَا تَفَرَّقُوا.
And hold fast by the covenant (rope) of Allah (Hablillah) all together and be not disunited… 3:103
ضُرِبَتْ عَلَيْهِمْ الذِّلَّةُ أَيْنَ مَا ثُقِفُوا إِلَّا بِحَبْلٍ مِنْ اللَّهِ.
Abasement is made to cleave to them wherever they are found, except under a covenant with Allah… (Surah Ale-Imran 3:112)
Many of the traditionists have said that it means those who remain steadfast on the promise of Allah are protected.
There is a tradition from Ayyashi that Imam Moosa Kazim (a.s.) said regarding the verse:
And hold fast by the covenant (rope) of Allah all together and be not disunited… (Surah Ale-Imran 3:103)
That Ali Ibne Abi Talib is ‘hablulallah matin’. It means the tight rope of Allah.
Another tradition from Imam Baqir (a.s.) says that the progeny of the Holy Prophet (S) is the rope of Allah, for whom Allah has commanded in this verse.
Also there is a tradition from Imam Sadiq (a.s.) that he said: We are the rope of Allah.
Ali Ibne Ibrahim has narrated that ‘Hablullah’ means the Oneness (Tawheed) of Allah and the Mastership (Wilayat) of Ahlul Bayt (a.s.).
Also there is a saying of Imam Baqir (a.s.) on the verse:
and be not disunited… (Surah Ale-Imran 3:103)
The Imam said that Allah was knowing that this nation would be separated from its Prophet and they will have difference with him. That is why he stopped them from the difference as the nation which was before them was prohibited. Therefore they were commanded that they should remain united on the Wilayat of Muhammad and his Progeny and should not disunite.
Ayyashi has narrated from Imam Sadiq (a.s.) that the ‘Habl of Allah’ is the book of Allah and ‘Habl-e-Naas’ is Ali Ibne Abi Talib (a.s.).
In Majalis of Shaykh Tusi and Manaqib of Ibne Shahr Aashob it is narrated from Imam Sadiq (a.s.) that: We are ‘Hablullah’ - the rope of Allah.