Sayyiduna Zaid bin Aslam narrates that I saw Sayyiduna Ibn Umar (may Allah be pleased with them both) praying with his button open, so I asked him about this, and he replied that he had seen the Prophet Muhammad (peace and blessings be upon him) doing so.
Hadith Referenceصحيح ابن خزيمه / جماع أبواب اللباس فى الصلاة / 779
The Imam, through his esteemed teacher Muhammad bin Yahya’s chain of narration, reports from Walid in a manner similar to the above. However, he did not mention the words that I asked him and said that I saw the Messenger of Allah (peace be upon him) praying with his button undone.
Hadith Referenceصحيح ابن خزيمه / جماع أبواب اللباس فى الصلاة / 780