The Prophet ﷺ said concerning Muawiya, "O Allah, make him a guide, rightly guided, and guide others through him."
عن النبي ﷺ أنه قال لمعاوية: اللهم اجعله هاديا مهديا واهد به.
Narrated by Tirmidhi (3842), Ahmad (17895), and Bukhari in Tarikh al-Kabir (7/326), all of them through various routes from Saeed bin Abdul-Aziz, from Rabia bin Yazid, from Abdul-Rahman bin Abu Umayra, who said, and then he related it. Tirmidhi said, "This is a hasan gharib hadith."I say, this is as he said. For Saeed bin Abdul-Aziz, who is Tanukhi, although he was the imam of the people of Syria, became confused in memory late in his life, and none of those who narrated this hadith from him can be shown to have heard it from him before or after that confusion set in. However, it is strengthened by what Tirmidhi narrated after it, from Abu Idris Khawlani, who said, When Umar bin Khattab removed Umayr bin Saad from Hims and appointed Muawiya in his place, the people said, "He removed Umayr and appointed Muawiya." Umayr said, "Do not mention Muawiya except with good, for I heard the Messenger of Allah ﷺ say, 'O Allah, guide through him.'"Tirmidhi said, "This is a gharib hadith, and Amr bin Waqid is considered daif." I say, this is as he said, though Ibn Adi said of him, "He is among those whose hadith is written down." By combining the two chains, the hadith becomes hasan according to Tirmidhi's own method, and that is why he graded it hasan. It is honor and virtue enough for Muawiya that the Prophet ﷺ took him as a scribe for revelation, just as he took him as a scribe for correspondence between himself and the Arabs, and this shows his truthfulness and trustworthiness in the eyes of the Prophet ﷺ.It is also narrated from Irbaz bin Sariya, as a saying of the Prophet, "O Allah, teach Muawiya the Book and reckoning, and protect him from punishment." Narrated by Ahmad (17152), Ibn Khuzayma (1938), and Ibn Hibban (3465), all of them through various routes from Yunus bin Sayf, from Harith bin Ziyad, from Abu Rahm Sammai, from Irbaz, who said, I heard the Messenger of Allah ﷺ calling people to the pre-dawn meal in the month of Ramadan, saying, "Come to the blessed meal." Then I heard him say, "O Allah, teach Muawiya the Book and reckoning, and protect him from punishment." This wording is Ahmad's.Harith bin Ziyad is from Syria, and Yunus bin Sayf alone narrated from him. Dhahabi said in Al-Mizan, "Unknown," and Abu Hatim said the same. Ibn Hajar said, "Weak in hadith." As for Ibn Hibban, he listed him among the reliable narrators according to his own method, even though Abu Hatim had said of him "unknown," so perhaps Ibn Hibban was not aware of that assessment.As for Haythami's statement in Majma (9/356), "Bazzar and Ahmad narrated it in a long hadith, and Tabarani as well, and it contains Harith bin Ziyad, whom I have found no one to have deemed reliable, and none narrated from him except Yunus bin Sayf, while the rest of its narrators are reliable, though there is some disagreement about some of them," this is an oversight on his part, for Ibn Hibban did list him among his reliable narrators, and Ibn Hibban is the very source Haythami relies upon for validating narrators.In any case, the chain of this hadith is daif, though its weakness is not severe. Perhaps Dhahabi, in Siyar (3/124), after mentioning the hadith of Irbaz, when he said, "This hadith has a strong corroborating witness," meant this hadith of Ibn Abu Umayra. Allah knows best what is correct.