Musannaf Ibn Abi Shayba 13:43

Jarir narrated to us, from ‘Ata’ ibn al-Sa’ib, from ‘Abdullah ibn Mughaffal, regarding a man who paid in advance (salam) one hundred dirhams for food. He took half of his advance in food, and the other half became difficult for him (to obtain). He said: "Do not take anything except your entire advance or your entire capital."