I have learnt that Mu‘āwiyah has written to you to deceive your wit and blunt your sharpness. You should be on guard against him because he is the Satan who approaches a believer from the front and from the back, from the right and from the left, to catch him suddenly in the hour of his carelessness and overcome his intelligence.
In the days of ‘Umar ibn al-Khaṭṭāb, Abū Sufyān  happened to utter a thoughtless point which was an evil suggestion of Satan, from which neither kinship is established nor entitlement to succession occurs. He who relies on it is like the uninvited guest to a drink-party or like the dangling cup (tied to a saddle).
قال السيد الرضى: فلمّا قرأ زياد الكتاب قال: شهد بها وربّ الكعبة، ولم يزل في نفسه حتى ادّعاه معاويةُ.
as-Sayyid ar-Raḍī says: When Ziyād read this letter he said, “By Allāh he has testified to it.” This point remained in his mind till Mu‘āwiyah claimed him (as his brother by his father).
قوله (عليه السلام): «كَالْوَاغِلِ الْمُدَفّعِ» الواغلُ: هوالذي يهجم على الشّرْب ليشرب معهم وَليس منهم، فلا يزال مُدفّعاً محاجزاً. و«النّوْط المُذَبْذَب»: هو ما يناط برحل الراكب من قعب أو قدح أو ما أشبه ذلك، فهو أبداً يتقلقل إذا حث ظهره واستعجل سيره.
Amīr al-mu’minīn’s word “al-wāghil” means the man who joins the drinking group so as to drink with them, but he is not one of them. He is therefore constantly turned out and pushed off. As for the words “an-nawṭu ’l-mudhabdhab”, it is a wooden cup or a bowl or the like attached to the saddle of the rider so that it dangles when the rider drives the beast or quickens its pace.
 Caliph ‘Umar sent Ziyād to Yemen for some encounter. When he returned after finishing the job he addressed a gathering which included Amīr al-mu’minīn, ‘Umar, ‘Amr ibn al-‘Āṣ and Abū Sufyān. Impressed with the speech ‘Amr ibn al-‘Āṣ said:
“What a good man! Had he been from the Quraysh he would have led the whole of Arabia with his stick.” Whereupon Abū Sufyān said, “He is from the Quraysh as I know who is his father.” ‘Amr ibn al-‘Āṣ enquired, “Who was his father?” Abū Sufyān said, “It is I.” History also conclusively holds that Ziyād’s mother Sumayyah, who was the slave-maid of al-Ḥārith ibn Kaldah and was married to a slave named ‘Ubayd, used to lead an immoral life in a quarter of aṭ-Ṭā’if known as Hāratu’l-Baghāyā, and immoral men used to visit her. Once Abū Sufyān also got to her through Abū Maryam as-Salūlī. As a result Ziyād was born. When ‘Amr ibn al-‘Āṣ heard this from Abū Sufyān, he asked why he had not declared it. Abū Sufyān pointed to ‘Umar and said that he was afraid of him, otherwise he would have declared him his own son. Although he would not have dared to do this, when Mu‘āwiyah acquired power he started correspondence with him because Mu‘āwiyah was in need of such persons who were intelligent and cunning and expert in machinations. In any case, when Amīr al-mu’minīn got information about this correspondence he wrote this letter to Ziyād wherein he warned him against Mu‘āwiyah so that he should not fall in the trap. But he did fall in his trap and joined Mu‘āwiyah and the latter declared him his brother by attaching him in his kin, although the Prophet had declared: The child goes to the (lawful) husband while the adulterer gets stones.