In one narration the words are: "He commanded me to show mercy to the poor and to keep sitting with them."
Imam Ahmad recorded it, and Imam al-Tabarani recorded something similar in al-Mu'jam al-Awsat. The narrators of one of Imam Ahmad's two chains are thiqat (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الزهد / 17908