Narrated AbudDarda' and Ubadah ibn as-Samit:
Khalid ibn Dihqan said: When we were engaged in the battle of Constantinople at Dhuluqiyyah, a man of the people of Palestine, who was one of their nobility and elite and whose rank was known to them, came forward. He was called Hani ibn Kulthum ibn Sharik al-Kinani. He greeted Abdullah ibn Zakariyya who knew his rank.
Khalid said to us: Abdullah ibn AbuZakariyya told us: I heard Umm ad-Darda' say: I heard AbudDarda' say: I heard the Apostle of Allah (peace_be_upon_him) say: It is hoped that Allah may forgive every sin, except in the case of one who dies a polytheist, or one who purposely kills a believer.
Hani ibn Kulthum ar-Rabi' then said: I heard Mahmud ibn ar-Rabi' transmitting a tradition from Ubadah ibn as-Samit who transmitted from the Apostle of Allah (peace_be_upon_him) who said: If a man kills a believer unjustly, Allah will not accept any action or duty of his, obligatory or supererogatory.
Khalid then said to us: Ibn AbuZakariyya transmitted a tradition to us from Umm ad-Darda' on the authority of AbudDarda' from the Apostle of Allah (peace_be_upon_him) who said: A believer will continue to go on quickly and well so long as he does not shed unlawful blood; when he sheds unlawful blood, he becomes slow and heavy-footed.
A similar tradition has been transmitted by Hani ibn Kulthum from Mahmud ibn ar-Rabi' on the authority of Ubadah ibn as-Samit from the Apostle of Allah (peace_be_upon_him).