It wasnarrated from 'Asim bin Sufyan Thaqafi that they went on thecampaign of Salasil, but no battle took place; they only took uptheirpositions. Then they came back to Mu'awiyah, and Abu Ayyuband 'Uqbahbin 'Amir were with him. 'Asim said:
"O Abu Ayyub,we have missed outon Jihad this year, and we were told that whoeverprays in the fourmosques will be forgiven his sins." He said: "Oson of my brother,shall I not tell you of something easier thanthat? I heard theMessenger of Allah (ﷺ) say: 'Whoever performsablution as he hasbeen commanded, and prays as he has beencommanded, will be forgivenhis previous (bad) deeds.'" He said:"(Did he not say it) like that, O'Uqbah?" He said: "Yes."
English reference: Vol. 1, Book 5, Hadith 1396
Arabic reference: Book 5, Hadith 1460