Musnad Ahmad 27:1775

Isma'il narrated to us, Yunus bin 'Ubayd informed us, from Ziyad bin Jubayr, who said: A man asked Ibn 'Umar while he was walking in Mina, saying: "I vowed to fast every Tuesday or Wednesday, and this day coincided with the Day of Sacrifice (Yawm al-Nahr). What is your opinion?" He said: "Allah the Exalted commanded the fulfillment of vows, and the Messenger of Allah (ﷺ) forbade—or he said: We were forbidden—to fast on the Day of Sacrifice." The man thought that he had not heard him, so he said: "I vowed to fast every Tuesday or Wednesday, and this day coincided with the Day of Sacrifice." He said: "Allah commanded the fulfillment of vows, and the Messenger of Allah (ﷺ) forbade us—or he said: We were forbidden—to fast on the Day of Sacrifice." He said: He did not add anything more to that until he ascended into the mountain.