مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3309
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn ‘Abbas (رضي الله عنه) said: Allah, may He be glorified and exalted, enjoined prayer when not travelling with four ruk'uhs, when travelling with two, and at the time of fear with one, on the lips of your Prophet (ﷺ).
Musnad Ahmad 3332Its isnad is saheeh, Muslim (687)]