Musannaf Ibn Abi Shayba 28:522

Abdullah ibn Numayr narrated to us, from al-A’mash, from Abd al-Malik ibn Maysarah, from al-Nazzal ibn Sabrah, who said: Ibn Mas’ud and Hudhayfah entered upon Uthman. Uthman said to Hudhayfah, "It has reached me that you said such and such." He said, "No, by Allah, I did not say it." When he went out, Abdullah [ibn Mas’ud] said to him, "What is the matter with you? Why did you not say it? I have heard you say it." He replied, "I am purchasing my religion, some of it with some of it, for fear that it might all be lost."