I heard the Messenger of Allah ﷺ say, "Whoever performs ablution and does so thoroughly, then walks to an obligatory prayer and prays it, his sins will be forgiven."
حدثنا حجاج ويونس قالا حدثنا ليث قال حجاج حدثني يزيد بن أبي حبيب عن عبد الله بن أبي سلمة ونافع بن جبير بن مطعم عن معاذ بن عبد الرحمن التيمي عن حمران مولى عثمان رضي الله عنه
سمعت رسول الله ﷺ يقول من توضأ فأسبغ الوضوء ثم مشى إلى صلاة مكتوبة فصلاها غفر له ذنبه
Its isnad is sahih. Abdullah bin Abu Salama Majishun is trustworthy. This isnad needs some clarification. The statement "Hajjaj said, Yazid bin Abu Habib narrated to me" should not be taken at face value as meaning that Hajjaj heard it directly from Yazid. Rather, Imam Ahmad intended to carefully preserve the exact wording of his teachers, as was his habit. He narrated the hadith from both Yunus and Hajjaj bin Muhammad, both of whom narrated from Layth bin Saad, from Yazid bin Abu Habib. But Hajjaj said in his narration, "from Layth, Yazid bin Abu Habib narrated to me," meaning that the one saying "narrated to me" is Layth, not Hajjaj.There are similar instances of this in the Musnad. Al-Hafiz has clarified examples of this in Tajil, pages 90-91. See also 409, 478, and 526.