Khabab came to Umar, and Umar said, "Come close. No one has more right to this seat than you, except Ammar."Khabab then began showing him the marks on his back left from the torture inflicted on him by the polytheists.
حدثنا علي بن محمد وعمرو بن عبد الله قالا حدثنا وكيع حدثنا سفيان عن أبي إسحق
جاء خباب إلى عمر فقال ادن فما أحد أحق بهذا المجلس منك إلا عمار فجعل خباب يريه آثارا بظهره مما عذبه المشركون
No references are available.
[Its chain of transmission is daif] though Busiri graded it sahih. Abu Ishaq narrated using "an", and his teacher's hadith is hasan. The hadith has daif corroborating narrations in Ibn Saad (3/165) and elsewhere.