This pillar, the fifth one down from the ‘Aisha’ pillar and in line with Bab-e-Jibraeel, is the approximate spot where the Prophet (ﷺ) originally led salah in Masjid-e-Nabwi. This was because when Masjid-e-Nabwi was first built the Qiblah was Masjid al-Aqsa in Jerusalem, and opposite to the Ka'bah in Makkah.
Around 16 months later the revelation of the Qur'an came to change the direction of the Qiblah to the Ka'bah. Masjid-e-Nabwi was then changed so salah was prayed the opposite side to how it was.