Humran. the freed slave of 'Uthman. said
I heard from 'Uthman b. 'Affan and he was in the courtyard of the mosque, when the Mu'adhdhin (announcer of the prayer) came to him at the time of afternoon prayer. So the ('Uthman) called for the ablution water and performed ablution and then said: By Allah, I am narrating to you a hadith. If there were not a verse in the Book of Allah, I would have never narrated it to you. I heard Allah's Messenger (ﷺ) say: If a Muslim performs ablution and does it well and offers prayer, all his (sins) daring the period from one prayer to another would be pardoned by Allah.
This hadith is also narrated on the authority with the same chain of transmitters and in the hadith of Abu Usama the words are
" He who performed the ablution well and then offered the obligatory prayer."
Humran reported when 'Uthman performed ablution he said
By Allah, I am narrating to you a hadith had there not been this verse in the Book of Allah. I would not have narrated it to you. Verily I heard the Messenger of Allah (ﷺ) say: Not a person is there who performed ablution, and did it well, then offered prayer, but his sins (which he committed) were not pardoned between the prayer that he offered and the next one. 'Urwa said: The verse is this:" Those who suppress the clear proofs and the guidance which We have sent down"... to His words:" the Cursers" (ii. 15).
'Amr b Sa'id b al-As reported
I was with Uthman, and he called for ablution water and said: I heard Allah's Messenger (ﷺ) say: When the time for a prescribed prayer comes, if any Muslim performs ablution well and offers his prayer with humility and bowing, it will be an expiation for his past sins, so long as he has not committed a major sin; and this applies for all times.
Humran, the freed slave of 'Uthman reported
I brought for Uthman b. 'Affan the ablution water. He performed ablution and then said: Verily the people narrate from the Messenger of Allah (ﷺ) a hadith. I do not know what these are. but (I know this fact) that I saw the Messenger of Allah (ﷺ) perform ablution like this ablution of mine and then he said: He who performed ablution like this, all his previous sins would be expiated and his prayer and going towards the mosque would have an extra reward. In the tradition narrated by Ibn 'Abda (the words are):" I came to Uthman and he performed ablution."
Abu Anas reported that Uthman performed ablution at Maqi'aid and said
Should I not show you the ablution performed by Allah's Messenger (ﷺ)? And he then washed (the different parts of the body) three times. 4" Qutaiba has added in his narration the words:" There were with him (with Uthman) Companions of Allah's Messenger (ﷺ)."
Humran b. Aban reported
I used to fetch water for 'Uthman for his purification. Never was there a day that he did not take a bath with a small quantity of water. And Uthman said: The Messenger of Allah (ﷺ) at the time of our returning from our prayer told us (certain things pertaining to purification). Mis'ar said: I find that it was afternoon prayer. He said: I do not know whether I should tell you a thing or keep quiet. We said: Messenger of Allah, tell us if it is good and if it is otherwise, Allah and His Apostle know better. Upon this he said: A Muslim who purifies (himself) and completes purification as enjoined upon him by Allah and then offers the prayers, that will be expiation (of his sins he committed) between these (prayers).
Jami' b. Shaddad reported
I heard Humran b. Aban narrate to Abu Burda in this very mosque during the governorship of Bishr that 'Uthman b. Alfan said: The Messenger of Allah (ﷺ) observed: He who completed ablution as Allah, the Exalted, enjoined upon him, his obligatory prayers would be explatious (for his minor sins that he would commit) during (the interval) between them. This hadith is transmitted by Ibn Mu'adh, and in the hadith narrated by Ghundar, the words" during the governorship of Bishr" are omitted and there is no mention of the obligatory prayers.
Humran, the freed slave of Uthman reported
One day Uthman b. Affan performed the ablution well, and then said: I saw Allah's Messenger (ﷺ) perform ablution, the best ablution, and then observed: He who performed ablution like this and then went towards the mosque and nothing (but the love of) prayer urged him (to do so), all his previous (minor) sins would be expiated.
Humran, the freed slave of 'Uthman b. 'Affan, reported on the authority of 'Uthman b. 'Affan that he heard Allah's Messenger (ﷺ) say
He who performed ablution for prayer and performed it properly and then went (to observe) obligatory prayer and offered it along with people or with the congregation or in the mosque, Allah would pardon his sins.