The Shia are those who submit to the Imams

My father, Allah have mercy upon him, related to us from Ali bin Ibrahim from his father from Ali bin Mabad from al-Hussein bin Khalid that Abu al-Hasan ar-Reza (a) said:

Our (true) Shia are those who submit to our orders, carry out our directives, and dissent from our enemies. He who does not enjoy such characteristics is not one of us.

The Shia were created from the same clay of the Imams

My father, Allah may have mercy upon him, narrated to us from Abdullah bin Ja’far from Ahmed bin Muhammad from Ibn Abi Nejran that he heard Abu al-Hasan (Imam ar-Reza) saying:

He who antagonizes our Shia is antagonizing us and whoever follows them is following us, because they are part of us. They were created from the same clay from which we were created. He who loves them is one of us, and whoever hates them is not with us. Our Shia see through the light of Allah, move about in the mercy of Allah, and will win the dignity of Allah. We feel the same pains that any of our Shia feels during ailment, we become grieved whenever any of our Shia becomes grieved, and we feel happy whenever any of our Shia feels happy.
No one of our Shia can be out of our auspices, whether he was in the east or the west of the earth. The debt that is left by any of our Shia is in our responsibility while the estate is his heirs.
Our Shia are those who offer the prayers, defray the zakat, perform the hajj to the Holy House of Allah, fast during the month of Ramadan, declare their loyalty to the Prophets household, and declare their disavowal of the enemies of the Prophets household. Those are the people of faith, God-fearing, piety, and devoutness. He whoever rejects them is rejecting Allah, because they are the true servants and the genuine disciples of Allah.
By Allah I swear, each individual of them will be granted (on the Day of Resurrection) the right to intercede for people as many as the individuals of the tribes of Rabeea and Madhar, out of Allahs honor to them.
He who honors a dissident is not Shiite

Muhammad bin al-Hasan bin al-Waleed related to us from Muhammad bin al-Hasan as-Saffar from Muhammad bin Easa bin Ubaid from Ibn Faddhal that Imam ar-Reza (a) said:
As for anyone who builds relations with somebody who disregards us, disregards somebody who builds good relations with us, praises somebody who reviles at us, or honors somebody who dissents from us, he is surely not one us and we are surely not from him.
The loyalty to the enemies of Allah

Muhammad bin Musa bin al-Mutawakkil narrated to us from Ali bin al-Hussein as-Sadabadi from Ahmed bin Muhammad bin Khalid from Ibn Faddhal that Imam ar-Reza (a) said:
He who follows the enemies of Allah will certainly antagonize the disciples of Allah, and whoever antagonizes the disciples of Allah will antagonize Allah Who will incumbently put him in the fire of Hell.
The affection for the Prophet household

Muhammad bin Musa bin al-Mutawakkil, Allah may have mercy upon him, narrated to us from Muhammad bin Yahya from Ahmed bin Muhammad al-Khezzaz that Imam ar-Reza (a) said:

Some of those who claim the affection for us the Prophets household- are more dangerous for our Shia than the ordeal of the Dajjal.
I asked: How do such people become dangerous?
The Imam (a) answered: They support our enemies and antagonize our followers. When this occurs, the right will be confused with the wrong and the whole matter will be perplexed. Then, there will be no distinction between the believers and the hypocrites.

The believer has characters from his Lord, Prophet, and Imam

My father, Allah may have mercy upon him, narrated to us from Ahmed bin Idris from Muhammad bin Ahmed bin Yahya bin Imran al-Ash’ari from Sahl bin Ziyad from al-Harith bin ad-Delhath (the servant of Imam ar-Reza) that Abu al-Hasan Reza (a) said:

A servant will not be a faithful believer before he learns three characters: one from the Lord, one from His Messenger, and one from the Imam. The character that he should learn from Allah is the concealment of secrets. Allah the Glorified says: He knows the unseen and He does not allow anyone to know His secrets… (72:28)

The character that he should learn from the Prophet (s) is that he should treat people courteously. Allah says: Take the surplus, preach the truth, and keep away from the ignorant ones. (7:199)

The character that he should learn from the Imam (a) is to be steadfast against situations of misfortune and crises. Allah says: and those who exercise patience in poverty and in distress. (2:177)

To deny the Ascension is to deny the Prophet
Muhammad bin Ibrahim bin Ishaq at-Taliqani, Allah may have mercy upon him, narrated to us from Ahmed bin Muhammad bin Saeed al-Hamadani from Ali bin al-Hasan bin Ali bin Faddhal from his father that Abu al-Hasan Ali bin Musa ar-Reza (a) said:
He who denies the Prophets Midnight Ascension is belying the Prophet.

Abdul-Wahid bin Muhammad bin Abdous al-Attar an-Nisapuri, Allah may please him narrated to us from Ali bin Muhammad bin Qutaiba from al-Fadhl bin Shathan that Ali bin Musa ar-Reza (a) said:

For anyone who declares the oneness of Allah, denies His being anthropomorphized, deems Him far above that whichever does not fit Him, declares that might, power, will, volition, creation, authority, and acts all are in the possession of Allah, believes that the acts of the servants (the planning for the acts, not their bringing into being) are created, declares that Muhammad (s) is the messenger of Allah and Ali (a) and the Imams who follow him are the arguments of Allah (against the creatures), supports their disciples, antagonizes their enemies, avoids committing the grand sins, believes in rajaa and the two mut, and has faith in the Prophets Midnight Ascension, the tomb interrogation, the Divine Pool, the right of intercession, the creation of Paradise and Hell, the Path, the Balance, the raising from the death, and the Resurrection, he is surely believer and one of our Shia the Shia of the Prophets household.

Source: Sifat ush-Shia by Shaikh Saduq