Anyone who knows of a tyrant’s injustice, or of a sinner’s sins, should lower his esteem for that person in his heart. In fact, it is required (wājib) to do so. This is because if something that is disapproved is committed by a person, it is certain to detract from his standing. So, sin should be disapproved. This is because sin may be ignored, or condoned, or disapproved. Obviously, if there is knowledge of the sin, then it cannot be ignored. And there can be no reason for condoning it. Therefore, it must be disapproved. Anyone’s transgression against the rights of God should be the same as transgression against your rights.
OBJECTION: Disapproval (karāha) is not a matter of choice. How, then, can it be required?
My reply is, ‘This is not so.’ This is because a lover, by nature, will dislike whatever his beloved dislikes and stand opposed to it. Then, anyone who does not dislike sins against God does not love God. Furthermore, only those who do not know God will not love Him. Knowledge [of God] is essential, and [thereafter] love of God is certain to follow. If someone loves Him, he will dislike what He dislikes and love what He loves. A complete explanation of this will be given in the Book of Love and Contentment.
OBJECTION: The scholars among our Predecessors used to visit rulers.
My reply is, ‘Yes, they did. But first learn how they used to visit, before you go [and do the same].’ It is related that Hishām b. ‘Abd al-Malik went to Mecca for the pilgrimage. When he arrived, he said, ‘Bring me someone from the Companions.’ When he was told that they had all passed away, he said, ‘Then, from among the Successors.’ And so Ṭāwūs al-Yamānī  was brought to him.
When Ṭāwūs entered, he removed his sandals at the edge of the carpet; and he did not greet him as Commander of the Faithful, saying instead no more than, ‘Peace be upon you.’ Nor did he use the agnomen . Then he sat by his side and said, ‘How are you, O Hishām?’ At that, Hishām flew into a towering rage, such that he considered killing him [Ṭāwūs]. But he was reminded, ‘You are within the sacred precincts of God [Mecca] and the sacred precincts of His Messenger [ﷺ], and that [killing] is not possible!’
So instead he replied, ‘O Ṭāwūs! What made you do what you have done? Ṭāwūs replied, ‘What did I do?’ Then Hishām grew even more angry and agitated. He said, ‘You took your sandals off at the edge of my carpet, but then you failed to kiss my hand. Nor did you greet me as Commander of the Faithful! Nor did you address me by my agnomen! Then you sat down beside me without first taking permission. Finally, you said, “How are you O Hishām!” ’
[Ṭāwūs] replied, ‘As for my removing my sandals by the edge of your carpet, I take them off five times a day when I go [to pray] before the Lord of All the Worlds. He has never punished me for doing so, or grown angry with me. As for your saying that I failed to kiss your hand, I once heard ‘Alī b. Abī Ṭālib, the Commander of the Faithful, (may God be pleased with him), say that is it is unlawful for anyone to kiss the hand of another unless it is a man kissing the hand of his wife in a surfeit of passion, or kissing the hand of his child in a surfeit of affection. As for your saying that I failed to greet you as Commander of the Faithful, well, not everyone is happy with your rule; so I disliked having to lie. As for your saying that I did not address you by your agnomen, God called His prophets and saints by their first name, saying, ‘O Dā’ūd!’ or ‘O ‘Īsā!’ or ‘O Yaḥyā!’ and He addressed His enemies, like Abū Lahab, by means of their agnomen. Now, as for your saying that I sat next to you, I heard ‘Alī, the Commander of the Faithful, (may God be pleased with him) say, ‘If you want to look at a person from among the inhabitants of the Fire, look at someone who is seated while others remain standing around him.’ At that, Hishām said, ‘Please advise me.’ [Ṭāwūs] said, ‘I heard ‘Alī, the Commander of the Faithful, (may God be pleased with him) say, “Verily in hell there are snakes like the summits of mountains and spiders the size of mules to bite [and sting] any amīr who is not just to his subjects.” ’ Then Ṭāwūs rose and left.
It is related that Sufyān al-Thawrī (may God be pleased with him) said, ‘I was brought into the presence of Abū Ja‘far al-Manṣūr at Mina and he said to me, “Tell us what you need.” I replied, “Fear God! For verily the earth is filled with injustice and discrimination!” So he dropped his head [in shame]. But again he raised it and said, “Tell us what you need?” I replied, “You have reached this stage [in the conquest of new territories] by means of the swords of the Emigrants and Helpers, yet their children are dying of starvation! So fear God, and see that they get their due!” So he dropped his head [in shame]. But again he raised it and said, “Tell us what you need?” So I replied, “When ‘Umar b. al-Khaṭṭāb performed the Pilgrimage, he said to his treasurer, ‘How much have I spent?’ The treasurer replied, ‘Ten and something dirhams.’ But here I see more opulence than a camel load of money could pay for!” Thereafter, Sufyān departed.
So that was how they used to visit rulers, even if they did so under duress. Indeed, they risked their own lives in order to avenge for the Almighty those who had been treated unjustly.
[Ghazālī on the Lawful and the Unlawful: Kitab al ḥalāl wa’l-ḥarām – Book XIV of the Revival of the Religious Sciences Iḥya’ ‘ulum al-dīn (translated with an introduction and notes by Shaykh Yusuf Talal DeLorenzo), Islamic Texts Society, Cambridge, 2014, pp. 214-217]
 Ṭāwūs ibn Kaysān al-Yamānī was named Ṭāwūs (which means ‘peacock’) because of his fine reading of the Qur’an. He was one of the scholars of the Tābi‘īn, a narrator of hadith and a companion of ‘Alī Zayn al-‘Abidīn (The Prophet’s (ﷺ) great grandson – son of Al-Ḥusayn bin ‘Alī (رضي الله عنه)). Ibn Ḥayyān said about him, “He was among the worshippers of the people of Yemen and one of the masters of the leading members of the next generation.” He performed the pilgrimage forty times. He was also a student of ‘Abdullāh ibn ‘Abbās (رضي الله عنه) and narrated ḥadīths from him. It was said he had met over 50 companions. He was the main teacher of ‘Umar ibn ‘Abdul ‘Azīz. He passed way in the year 106H (723 CE).
 “To do so would have been another way of showing respect, by saying, for example, O Abū Sulayman! To have neglected to address Hishām either by his title or by his agnomen was to have emphasised the fact that his words were chosen carefully, and that Ṭāwūs had meant to slight the ruler.” [Shaykh Yusuf’s footnote]
 “Sufyān ibn Sa‘īd ibn Masrūq Abū ‘AbdAllah al-Thawrī al-Muḍarī al-Kūfī (97-161) [716-778 CE], the Godfearing, wise, grief-stricken, Mujtahid Imām, was “Commander of the Believers in Ḥadīth” – the highest level in ḥadīth Mastership –, ‘Shaykh al-Islām, the Imam of ḥadīth Masters, the leader of the practicing Ulema in his time, the author of the Jāmi‘ ’ (al-Dhahabi)…‘If I had been asked to choose someone to lead this Umma [as a Caliph] I would have chosen Sufyān al-Thawrī’ (Al-Awzā‘ī)”