Riyad as-Salihin (The Meadows of the Righteous)
by Imam Nawawi
166. Chapter: On the Recommendation to set out on a journey on a Thursday at the beginning of the day
956. Ka'b ibn Malik said, " The Prophet, may Allah bless him and grant him peace, left on the expedition of Tabuk on a Thursday. He liked to set out on Thursdays." [Agreed upon]
In one variant, "Rarely did the Messenger of Allah, may Allah bless him and grant him peace, set out on other than a Thursday."
957. Sakhr ibn Qada'a al-Ghamidi the Companion reported that the Messenger of Allah, may Allah bless him and grant him peace, said, "O Allah, bless our community in its mornings." When he sent out an expedition or an army, he sent them forth at the beginning of the day. Sakhr was a merchant. He used to send out his goods at the beginning of the day and he became wealthy and had a lot of property." [Abu Dawud and at-Tirmidhi]