Accept the truth, whoever it comes from

It is reported that a man came to ʿAbdullāh b. Mas’ūd – Allāh be pleased with him – and asked, “Teach me some comprehensive and beneficial words.” He replied, “Worship Allāh and do not associate any partners with Him, and be with the Qur’ān wherever it is. And whoever comes to you with some truth – whether he is young or old, even if he is hated by you – then accept [that truth]. And whoever comes lying to you – even if he is beloved and close – then reject it from him.”

Abū Bakr Al-Kharā`iṭī, Masāwī Al-Akhlāq wa Madhmūmihā p72.