From Sahih Bukhari (Hadith 1563):
Narrated Marwan bin Al-Hakam:I saw `Uthman and `Ali. `Uthman used to forbid people to perform Hajj-at-Tamattu` and Hajj-al-Qiran (Hajj and `Umra together), and when `Ali saw (this act of `Uthman), he assumed Ihram for Hajj and `Umra together saying, "Labbaik for `Umra and Hajj," and said, "I will not leave the tradition of the Prophet (ﷺ) on the saying of somebody
Reference: Bukhari 1563