Hadith No: 1
Ibn Manzur - Lisan al-Arab - Letter Shiin - Shi'ah
Volume: (8) - Page Number: (189)
[The text is lengthy, so only the relevant excerpt is provided here]
- .... And this name, namely the Shi'ah, has prevalently been used to refer to those who hold Ali and his family (may peace be upon them all) in high regard, until it has become a specific name for them. Thus, if it is said: ( "So-and-so is one of the Shi'ah" ), it is understood that he is one of them.

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Reference: Lisaan al Arab Book 8

Hadith No: 2
Al-Zubaidi - Taj al-Urus min Jawahir al-Qamus - Shi'ah
Volume: (21) - Page Number: (303)
[The text is lengthy, so only the relevant excerpt is provided here]
- .... And this name has come to be associated with anyone who follows Ali and his family (peace be upon them) altogether, until it has become a specific name for them. Thus, if it is said that so-and-so is from the Shi'ah, it is understood that they are one of them. And in the doctrine of the Shi'ah, etc., means in their view, and the original of this is from "mushayiah," which means compliance and following.

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Reference: Taaj al Uroos min Jawahar al Qamus Book 21

Hadith No: 3
Al-Shahrastani - al-Milal wa al-Nihal
Chapter One: The Muslims - Section Six: The Shi'a - Introduction
Volume: (1) - Page Number: (146)
[The text is lengthy, so only the relevant excerpt is provided here]
- .... The Shi'a are those who supported Ali and affirmed his Imamate and Caliphate through explicit and implicit نص and وصاية. They believe that the Imams will not come from his descendants, and if they do, it would be due to an injustice from another or an act of taqiyya from him.

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Reference: Al Milal wa Nahl Book 1

Hadith No: 4
Ibn Khaldun - Tarikh Ibn Khaldun - Volume One: On the Nature of Civilization in Creation
And what occurs within it of the nomadic and the sedentary, dominion and acquisition, livelihood and crafts, sciences, and similar matters, along with the underlying causes and reasons for all of that
Chapter Three of Volume One: On General States, Sovereignty, and the Caliphate
And the Ranks of Authority, and the circumstances that arise in all of this, including principles and supplements
Section Twenty-Seven: On the Beliefs of the Shi'a Regarding the Ruling of Imamate
Part: (1) - Page Number: (246)
[The text is lengthy, so only the relevant passage is excerpted here]
- .... Know that "Shi'a," in its linguistic sense, means companions and followers, and it is used in the terminology of the theologians and scholars of both the later and earlier generations to refer to the followers of Ali and his sons.

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Reference: Tarikh Ibn Khaldoon Book 1