Abu 'Abd al-Rahman al-Sulami stated, "Muhammad ibn 'Ali al-Qassab of Baghdad was the master (ustadh) of Junayd. Junayd [himself] used to say, 'People connect me with Sari (that is to say, Sari al-Saqati), while my master was Muhammad al-Qassab.' Abu Ja'far al-Qassab died in the year 275 AH/ 888-89 CE."
Muhammad ibn Sa'id reported that he heard Junayd saying, "Our master, Abu Ja'far al-Qassab was asked 'Why are your companions cut off from people?' He answered, 'Because of three of their traits: first, God is not pleased with whatever they possess, and if God were to be pleased with their possessions, God would allow their possessions to rule them; second, it does not please God to place their virtues in their appearance, and were this not the case, God would confuse them by means of their appearance; and third they are folk who travel only toward God, so God has obstructed them from reaching anything but God, keeping them for God alone."