Saeed bin Musayab reported,

Uthman set out for Hajj, and when he was partway along the road, it was reported to Ali, may Allah be pleased with them both, that Uthman had forbidden combining Umra with Hajj as tamattu.So Ali said to his companions, "When he sets off, you set off as well." Then Ali and his companions entered the state of ihram for Umra, and Uthman did not say anything to him about it.Ali said to him, "Was I not informed that you had forbidden combining Umra with Hajj as tamattu?"Uthman replied, "Yes."Ali asked, "Did you not hear the Messenger of Allah ﷺ perform tamattu?"He answered, "Yes."

حدثنا يحيى عن ابن حرملة قال

سمعت سعيدا يعني ابن المسيب قال

خرج عثمان رضي الله عنه حاجا حتى إذا كان ببعض الطريق قيل لعلي رضوان الله عليهما إنه قد نهى عن التمتع بالعمرة إلى الحج فقال علي رضي الله عنه لأصحابه إذا ارتحل فارتحلوا فأهل علي وأصحابه بعمرة فلم يكلمه عثمان رضي الله عنه في ذلك فقال له علي رضي الله عنه ألم أخبر أنك نهيت عن التمتع بالعمرة قال فقال بلى قال فلم تسمع رسول الله ﷺ تمتع قال بلى