مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2121
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated from Ibn 'Abbas (رضي الله عنه) that Allah (may He be glorified and exalted) enjoined the duty of prayer on the lips of your Prophet (ﷺ), four (rak'ahs) for the non-traveller, two rak’ahs for the traveller, and one rak'ah for the one who is in a state of fear.
Musnad Ahmad 2124Its isnad is saheeh, Muslim (687)]