Musnad Ahmad 1227:13

Ishaq, meaning Ibn al-Taba', narrated to us, he said: Ibn Lahi'ah narrated to us, from Yazid ibn Abi Habib, from al-Zuhri, from Ibn Ka'b ibn Malik, from his father: "That the Messenger of Allah, peace and blessings of Allah be upon him, when he intended to travel, he would not travel except on a Thursday."