Abdullah bin Abbas reported,

Regarding Allah's statement, "And remember when those who disbelieved plotted against you to restrain you" [Anfal 8:30], he said:Quraysh held a council one night in Makkah. Some of them said, "When morning comes, bind him in chains," meaning the Prophet ﷺ.Others said, "No, kill him."Still others said, "No, expel him."Allah informed His Prophet ﷺ of this, so Ali slept in the Prophet's bed that night, while the Prophet ﷺ left and made his way to the cave. The polytheists spent the night keeping watch over Ali, thinking he was the Prophet ﷺ.When morning came, they rushed at him, but when they saw it was Ali, Allah turned their plot back on them. They said, "Where is this companion of yours?"He replied, "I do not know."They followed his tracks, but when they reached the mountain, the trail became confused for them. They climbed the mountain and passed by the cave, where they saw a spider's web across its entrance. They said, "If he had entered here, there would be no spider's web at its mouth."He remained inside it for three nights.

حدثنا عبد الرزاق حدثنا معمر قال وأخبرني عثمان الجزري أن مقسما مولى ابن عباس أخبره

عن ابن عباس

في قوله {وإذ يمكر بك الذين كفروا ليثبتوك} قال تشاورت قريش ليلة بمكة فقال بعضهم إذا أصبح فأثبتوه بالوثاق يريدون النبي ﷺ وقال بعضهم بل اقتلوه وقال بعضهم بل أخرجوه فأطلع الله عز وجل نبيه ﷺ على ذلك فبات علي على فراش النبي ﷺ تلك الليلة وخرج النبي ﷺ حتى لحق بالغار وبات المشركون يحرسون عليا يحسبونه النبي ﷺ فلما أصبحوا ثاروا إليه فلما رأوا عليا رد الله مكرهم فقالوا أين صاحبك هذا قال لا أدري فاقتصوا أثره فلما بلغوا الجبل خلط عليهم فصعدوا في الجبل فمروا بالغار فرأوا على بابه نسج العنكبوت فقالوا لو دخل هاهنا لم يكن نسج العنكبوت على بابه فمكث فيه ثلاث ليال