مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3300
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn 'Abbas (رضي الله عنه) said: The Messenger of Allah (ﷺ) put Zuhr and ‘Asr together, and Maghrib and ‘Isha', in Madinah when there was no fear and no rain. I (the narrator) said to Ibn 'Abbas: Why did he do that? He said: So as not to make things difficult for his ummah.
Musnad Ahmad 3323Its isnad is saheeh, Muslim (705)]