The Messenger of Allah ﷺ sent Muaz bin Jabal to Yemen and gave him counsel. Among his instructions was, "Beware of taking the most prized of their wealth, and guard yourself against the supplication of the oppressed, for there is no barrier between it and Allah."
بعث رسول الله ﷺ معاذ بن جبل إلى اليمن، فأوصاه، وكان من وصيته: إياك وكرائم أموالهم، واتق دعوة المظلوم، فإنه ليس بينه وبين الله حجاب.
Bukhari narrated it in the Book of Zakat (1496) and Muslim in the Book of Faith (19), both from the hadith of Zakariya bin Ishaq, from Yahya bin Abdullah bin Sayfi, from Abu Mabad, the freed slave of Ibn Abbas, from Ibn Abbas, who mentioned it in a long hadith.