مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2793
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated from Ibn ‘Abbas (رضي الله عنه) that The Prophet (ﷺ) used to pray on a small mat of palm fibre.
Musnad Ahmad 2813Saheeh because of corroborating evidence]