مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3388
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated from Ibn 'Abbas (رضي الله عنه) We travelled with the Messenger of Allah (ﷺ) between Makkah and Madinah, not fearing anything but Allah, may He be glorified and exalted, and praying two rak'ahs (i.e., shortening the prayers).
Musnad Ahmad 3411A saheeh hadeeth]