Musnad Ahmad 937:212

Yahya ibn Sa'id narrated to us, from Shu'bah, Abu 'Imran al-Jawni narrated to us, from 'Abdullah ibn al-Samit, who said: When Abu Dharr arrived to 'Uthman from al-Sham, he said: My beloved (peace be upon him) commanded me with three things: "Listen and obey, even if it is to a slave whose limbs are mutilated. And if you make broth, increase its water, then look to a household among your neighbors and provide them with some of it in kindness. And perform the prayer at its time; if you find that the Imam has already prayed, then you have secured your prayer, and if not, it is a supererogatory prayer."