Yazid bin Abi Sufyan narrates that when Sayyiduna Abu Bakr Siddiq (may Allah be pleased with him) sent me towards Syria, he advised me, saying: "Yazid! You have some relatives, and it is possible that, because you are the commander of the army, you may give preference to your relatives. Of all things, this is what I fear most regarding you, because the Messenger of Allah (peace and blessings be upon him) said: Whoever is made responsible for any collective affair of the Muslims and, by giving preference to others, appoints someone to a position, the curse of Allah is upon him. Allah will not accept any obligatory or voluntary act of worship from him, until He admits him into Hell. And whoever gives someone protection in the name of Allah, and then unjustly breaks the promise of protection given in Allah’s name, the curse of Allah is upon him, or he said: Allah is free from him."