What are the sayings of scholars regarding Ali ibn Ahmad al-Kharaqani al-Bistami, one of the luminaries of the Naqshbandi Sufi order?

Al-Dhahabi and Al-Sam'ani wrote biographies of Abu Al-Hasan Ali ibn Ahmad Al-Kharqani Al-Bistami, describing him as a exemplary ascetic and the shaykh of his era, a man of miracles and spiritual states. In his early life, he used to rent out donkeys, then Allah opened up to him. Sultan Mahmud visited him and embraced him after Al-Kharqani had advised him, but he did not accept any money from him. Al-Kharqani passed away on the day of Ashura in the year 425 AH at the age of 73. He was not Naqshbandi, for the Naqshbandiyya is a Sufi order that emerged after his death, founded by Baha al-Din Muhammad al-Bukhari, who died in 791 AH.