It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) appointed Sayyiduna Zayd bin Harithah (may Allah be pleased with him) as commander in the expedition of Mu'tah and said: "If Zayd is martyred, then Ja'far, and after Ja'far, Abdullah bin Rawahah will be the commander." Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: I too was in that expedition. We found Sayyiduna Ja'far (may Allah be pleased with him) slain, and on his body there were more than 90 wounds from swords and arrows.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16596
Sayyiduna Anas bin Malik (may Allah be pleased with him) said that the Prophet (peace and blessings be upon him) sent Zayd, Ja'far and Abdullah bin Rawahah (may Allah be pleased with them) with an army and made Zayd bin Harithah (may Allah be pleased with him) the commander. All of them were martyred, and the Prophet (peace and blessings be upon him) announced the martyrdom of all three before the news arrived. He said: "Zayd took the banner and was martyred; then Ja'far, and then Abdullah bin Rawahah took the banner, and they were both martyred too. Then one of the swords of Allah, Khalid bin al-Walid, took the banner." He (peace and blessings be upon him) was telling this while tears flowed from his (peace and blessings be upon him) eyes.
This hadith is evidence that one who is fit for leadership can become the deputy, and if he sees that no one else is fit, a man can become the leader even without being appointed, as Sayyiduna Khalid bin al-Walid (may Allah be pleased with him) did.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16597
Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said that the Prophet (peace and blessings be upon him) sent out an army and appointed Sayyiduna Usamah (may Allah be pleased with him) as its commander. The people disliked his leadership and criticised it, so the Prophet (peace and blessings be upon him) said: "You are criticising his leadership; this is nothing new, for before this you did the same regarding his father. By Allah! He is most deserving of leadership; his father was the most beloved of all people to me, and now after him this one is the most beloved to me."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16598
Sayyiduna Abu Musa al-Ash'ari (may Allah be pleased with him) said that the Prophet (peace and blessings be upon him) sent me and Sayyiduna Mu'adh (may Allah be pleased with him) to Yemen and said: "Cooperate with each other, make things easy and do not make them difficult, create love and do not spread aversion."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16599
Umm Husayn al-Ahmasiyyah (may Allah be pleased with her) said: I heard the Prophet (peace and blessings be upon him) saying: "Even if an Abyssinian slave is appointed as governor over you, obey him while remaining within the bounds of the Book of Allah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16600
Sayyiduna Anas bin Malik (may Allah be pleased with him) said that Sayyiduna Qays bin Sa'd (may Allah be pleased with him) was, in relation to the Prophet (peace and blessings be upon him), like the chief of police in relation to a governor, overseeing his affairs.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قتال أهل البغي / 16601