مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3164
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn Abi Mulaikah said: Ibn ‘Abbas (رضي الله عنه) wrote to me (saying): The Messenger of Allah (ﷺ) said: "If people were to be given on the basis of what they claim, some people would claim the lives and wealth of others. But the one against whom a claim is made should swear an oath.”
Musnad Ahmad 3188Its isnad is saheeh, al-Bukhari (2514) and Muslim (1711)]