[And if you do not believe me] meaning: do not trust me, [then keep away from me] until Allah judges between me and you.
Muhammad said: It is said the meaning is: If you do not believe me, then do not be against me nor with me.
﴿وَإِن لم تؤمنوا لي﴾ تصدقوني ﴿فاعتزلون﴾ حَتَّى يحكم الله بيني وَبَيْنكُم.
قَالَ محمدٌ: قيل: الْمَعْنى: فَإِن لم تؤمنوا لي؛ فَلَا تَكُونُوا عَليّ وَلَا معي.