مُسْنَدُ أَحْمَدَ
Musnad Ahmad 1952
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn "Abbas said: The Messenger of Allah (ﷺ) put Zuhr and ‘Asr, and Maghrib and "Isha", together in Madinah when there was no state of fear or rain. It was said to Ibn ‘Abbas: What was the purpose of that? He said: He did not want to cause any hardship for his ummah.
Musnad Ahmad 1953Sahih (Darussalam) [ Muslim (705)]