This is the Bayda where people tell lies about the Messenger of Allah ﷺ. By Allah, the Prophet ﷺ entered ihram only from beside the mosque.
حدثنا سفيان عن موسى بن عقبة عن سالم قال كان
هذه البيداء التي يكذبون فيها على رسول الله ﷺ والله ما أحرم النبي ﷺ إلا من عند المسجد
Its isnad is sahih, and the two Shaykhs also narrated it, as noted in al-Muntaqa 2368. The masjid referred to is the masjid of Zulhulayfa, as is made clear in some of its narrations recorded by the two Shaykhs and others.Shawkani said, 5:35-36, "This Bayda lies beyond the two waymarkers of Zulhulayfa, for one ascending from the valley. This was stated by Abu Ubayd Bakri and others.Whenever Ibn Umar was told that ihram was to be entered from the Bayda, he would object to this, saying, 'The Bayda, where you people lie about the Messenger of Allah ﷺ?' meaning by your statement that he entered ihram from there, when in fact he entered ihram from the masjid of Zulhulayfa.He is alluding to the statement of Ibn Abbas recorded by Bukhari, that he ﷺ mounted his riding beast and once it stood level on the Bayda, he entered ihram, and also to the hadith of Anas mentioned in this chapter."By "lying" here is meant reporting something in a way that contradicts what actually happened, even if it was not done intentionally. See what has already been discussed in the Musnad of Ibn Abbas, 2296, 2528, 3149, 3525.