The conditions for imams

It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "The imam of a people is their delegate and representative before Allah, the Mighty and Majestic, so put forward the most virtuous and best among you (to lead the prayer)."
Because of the presence in its chain of matruk (abandoned) and da'if (weak) narrators such as Dawud bin al-Muhabbar and Anbasah bin Abd al-Rahman, this hadith is extremely weak in its chain.

It is narrated from Abu Salih (may Allah have mercy on him) that "Sayyiduna Mu'adh (may Allah be pleased with him) used to pray the Fajr prayer with the Prophet (peace and blessings be upon him), then he would return and lead his companions in prayer."
This report is mursal.

It is narrated from Sayyiduna Salman al-Farisi (may Allah be pleased with him) that the people of his tribe put him forward to lead them in prayer, but he refused, until they (with great insistence) pushed him forward. When he had led them in prayer, he asked: "Are all of you pleased (with my leading you)?" They said: Yes. So he (may Allah be pleased with him) said: 'Al-hamdu lillah' (All praise is for Allah). I certainly heard the Messenger of Allah (peace and blessings be upon him) saying: "There are three people whose prayer is not raised (for acceptance): a woman who leaves her house without her husband's permission, a slave who has run away (from his master), and a man who leads a people in prayer while they dislike him."
Imam Ibn Abi Shaybah recorded this report in his Musannaf, and hadith of similar meaning are also found in other books of Sunan, which contain the warning that the prayer of such an imam is not accepted when those following him dislike him because of some religious defect or fault.

It is narrated from al-Hajjaj (may Allah have mercy on him) that "Sayyiduna Ali (may Allah be pleased with him) used to dislike that a person who had performed tayammum should lead in prayer those who had performed ablution (wudu)."
Imam Musaddad (may Allah have mercy on him) recorded this athar in his Musnad.

Sa'd bin Ibrahim (may Allah have mercy on him) narrates from his father that "Sayyiduna Mu'awiyah (may Allah be pleased with him) led the people in prayer while wearing only a single shirt."
This athar is evidence for the juristic ruling that if a single garment (a shirt) suffices to cover the religiously required awrah, then praying and leading the prayer in it is permissible without dislike.

It is narrated from Abu al-Ahwas and Damrah that the Prophet (peace and blessings be upon him) said: "O Abu Ubaydah! After me, let no one ever lead the prayer sitting."
Imam al-Harith recorded this hadith; its chain contains Abu Bakr bin Abi Maryam, who is a da'if (weak) narrator. Moreover, this report is mursal, since Abu al-Ahwas and Damrah are Successors who transmitted it directly from the Prophet (peace and blessings be upon him).