I heard the Messenger of Allah ﷺ say, "A man may finish his prayer and have only a tenth of it recorded for him, or a ninth, an eighth, a seventh, a sixth, a fifth, a fourth, a third, or a half."
سمعت رسول الله ﷺ يقول: إن الرجل لينصرف، وما كتب إلا عشر صلاته، تسعها، تمنها، سبعها، سدسها، خمسها، ربعها، تلتها، نصفها.
Abu Dawud (796) narrated it, saying, Qutayba bin Saeed narrated to us, from Bakr - meaning Ibn Mudar, from Ibn Ajlan, from Saeed Maqburi, from Umar bin Hakam, from Abdullah bin Anama Muzani, from Ammar bin Yasir, and he mentioned something similar. Imam Ahmad (18894) also narrated it from Safwan bin Isa, and Tahawi in his Mushkil (1103) through the route of Haywa bin Shurayh, both of them from Ibn Ajlan with the same wording.Its chain is hasan because of Muhammad bin Ajlan, for his hadith is hasan. As for Abdullah bin Anama, there is disagreement about him. It is said that he was a companion who witnessed the conquest of Alexandria. However, Ibn Manda said, "He was a companion, but no narration is known from him," meaning from the Prophet ﷺ. This does not preclude him narrating from someone else, as is the case here. He has been corroborated by Ibn Las Khuzai, who said, Ammar bin Yasir entered the masjid and prayed two light and complete rakahs there. He said, then he sat down, so we got up and went to him and sat beside him. Then we said to him, "You made these two rakahs of yours very light, Abu Yaqzan!" He said, "I hurried through them to beat Satan before he could intrude on them." He said, and he mentioned the hadith.Imam Ahmad (18323) narrated it from Yaqub, my father narrated to us, from Muhammad bin Ishaq, Muhammad bin Ibrahim bin Harith Taymi narrated to me, from Umar bin Hakam bin Thawban, from Ibn Las Khuzai with the same wording, except that Imam Ahmad did not mention the wording of the hadith itself there, but rather mentioned it in another place in the hadith of Abdullah bin Anama, as previously given in the wording of Abu Dawud. The wording of Imam Ahmad is, I saw Ammar bin Yasir enter the masjid and make the prayer light. He said, when he came out, I went up to him and said, "Abu Yaqzan, you made it light." He said, "Did you see me fall short in any of its requirements?" I said, "No." He said, "I hurried through it to beat the negligence brought on by Satan. I heard the Messenger of Allah ﷺ say," and he mentioned the hadith as given before.Ahmad (18894) narrated it from Safwan bin Isa, who said, Ibn Ajlan informed us with the same wording as before.The second chain in Imam Ahmad is hasan because of Muhammad bin Ishaq, who has clearly stated that he heard directly, which removes the suspicion of tadlis from him, and his narration is hasan when he states it clearly.Ibn Las, also called Abu Las, was a companion. Bukhari related from him in a mualaq form. He is well known by his kunya, and his actual name is not known. Al-Hafiz mentioned him in Al-Isabah (4/168) in the chapter on kunyas, in the first section. Ibn Abdul-Barr said in Al-Istiab, "He was a companion counted among the people of Madinah. Umar bin Hakam bin Thawban narrated from him."The hadith has other routes as well, and the one I have mentioned is the most sahih of them. For more, see Sunan al-Kubra (2/281).