Abdullah bin Anamah (may Allah have mercy on him) narrates that Sayyiduna Ammar bin Yasir (may Allah be pleased with him) came into the mosque and offered a brief prayer. I said: O Abu al-Yaqzan, you prayed very briefly. He said: Did you see me fall short in anything of the prayer? The reason I hurried was so that Satan would not make me forgetful in the prayer. I heard the Messenger of Allah (peace and blessings be upon him) say: "A man finishes his prayer and there is written for him a tenth of the prayer's reward, a ninth, an eighth, a seventh, a sixth, a fifth, a quarter, a third, and sometimes a half."
(b) Umar bin Abi Bakr bin Abd al-Rahman (may Allah have mercy on him) narrates from his father that Ammar bin Yasir (may Allah be pleased with him) prayed two rak'ahs, and Abd al-Rahman bin al-Harith (may Allah have mercy on him) said: O Abu al-Yaqzan, I think you have made the prayer brief.
(c) Abu al-Yasar (may Allah have mercy on him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Among you is one who prays the complete prayer, and one who prays half of it, one a third, one a quarter, and one a fifth," until he mentioned even the tenth part.
(d) Abu Hurayrah (may Allah be pleased with him) narrates that the Prophet (peace and blessings be upon him) said: "A servant prays, and there is written for him a tenth of his prayer, a ninth, an eighth, a seventh part, and for some the complete reward of his prayer is written."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3527