Musnad Ahmad 379:1

Abu al-Nadr narrated to us, he said: al-Mubarak narrated to us, he said: al-Hasan narrated to us, that a sheikh from Banu Sulayt informed him, he said: I came to the Prophet, peace and blessings of Allah be upon him, to speak to him regarding captives of ours taken during the Pre-Islamic period (Jahiliyyah). I found him sitting, and there was a circle that had surrounded him, and he was speaking to the people. He was wearing a thick Qatari waist-wrapper (izar). He said: I heard him saying, while he was pointing with his finger: "The Muslim is the brother of the Muslim; he does not wrong him, nor does he forsake him. Taqwa (piety/fear of Allah) is here, Taqwa is here." He said: Meaning, in the heart.