Musannaf Ibn Abi Shayba 13:65

Marwan ibn Mu'awiyah narrated to us, from al-Zibriqan al-Sarraj, who said: I asked Abdullah ibn Mughaffal about the *salam* (forward sale) transaction: "Should one take a pledge (*rahn*) or a guarantor (*qabil*) for it?" He replied: "Secure what is yours."