مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3269
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) that The Messenger of Allah (ﷺ) to said: "The one against whom a claim is made should swear an oath. If people were to be given on the basis of what they claim, people would claim a lot of wealth and lives.”
Musnad Ahmad 3292lts isnad is saheeh, al-Bukhari (2514) and Muslim (1711]]