Musnad Ahmad 26:361

'Affan narrated to us, Hammad narrated to us, 'Ata' ibn al-Sa'ib informed us, from Ibn Adhnan, who said: I lent 'Alqamah two thousand dirhams. When his stipend came out, I said to him: "Pay me back." He said: "Delay me until next year." I refused him, and I took it [the money]. He said: I came to him later, and he said: "You have troubled me, and you have withheld [the money] from me." I said: "Yes, it is your own doing." He said: "And what is my affair?" I said: "You narrated to me from Ibn Mas'ud that the Prophet, peace and blessings of Allah be upon him, said: 'Indeed, a loan (al-salaf) runs the course of half of charity.'" He said: "Yes, it is indeed like that." He said: "Then take it now."