مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2155
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn 'Abbas (رضي الله عنه) said: The people started asking about prayer when travelling. He said: When the Messenger of Allah (ﷺ) departed from his family, he would only pray two rak'ahs [in a prescribed four rak'ah] prayer until he came back to his family.
Musnad Ahmad 2159Its isnad is saheeh]