This is the website I was just looking at:
NITAAI ( NITyananda Gauranga Hare Krishna NAAma BhaktI ) Yoga By HH Bhaktiratna Sadhu Swami Gaurangapada
tatah kalau sampravritte sammohaya sura-dvisham
buddho namnanjana-sutah kikateshu bhavishyati
(Srimad-Bhagavatam 1.3.24)
“Thereafter, in the twenty-first manvantara at the beginning of Kali-yuga, the Lord will appear as Lord Buddha, the son of Anjana, in Kikata Pradesa (the province of Gaya-Bihar), just for the purpose of deluding those who are envious of the faithful demigods.”
According to Sri Visvanatha Cakravarti Öhakura’s commentary:
anjana suto ’jina sutasceti pathadvayam
kikateshu madhye gayapradese
“The names Anjanasuta and Ajinasuta can both be found in the above verse. The province of Gaya has been called Kikateshu.”
It is written in the 29th Verse, 36th Chapter of Sri Nrisimha Purana:
kalau prapte yatha buddho bhavennarayana prabhuh
“Lord Narayana appeared as Buddha when the age of Kali started.”
This clearly implies that Lord Buddha appeared five thousand years ago. The following verse can be found in the second paragraph of Nirnaya-sindhu:
jyaishtha sukladitiyayam buddhajanma bhavishyati
“Buddha will take birth on the 2nd day of the sukla-paksha of the month of Jyaishtha.”
In Sri Madhvacarya’s commentary on Verse 1.3.24 of Srimad-Bhagavatam, from his book Bhagavata-tatparya, the following quotation from Brahmanda Purana has been referred to:
mohanartham danavanam balarupi pathisthitah
putram tam kalpayamasa mudhabudhirjinah svayam
tatah sammohayamasa jinadyana suramsakan
bhagavan vagbhirugrabhirahimsa vacibhirharih
(Brahmanda Purana)
“In order to delude the demons, He (Lord Buddha) was present in the form of a child on the way while the fool, Jina (a demon), imagined Him to be his son. Later on, Lord Sri Hari (as avatara-Buddha) expertly deluded Jina and other demons by His strong words of non-violence.”
There is an authentic Buddhist book, Lankavatara-sutra, in which Ravana, the king of Lanka, prays to Jina’s son, the ancient Lord Buddha, and to all the Buddhas and Buddhas’ sons who would appear in the future, via this eulogy (stava):
atha ravano lankadhipatih gathagiten anugayati sma lankavatarasutram vaih purvabuddhanuvarnitam smarami purvakaih buddhairjinaputra-puraskritaih putrametannigadyate bhagavanapi bhashatam bhavishyantyanapate kale buddha buddhasutasca ye
Therefore, this source leaves no doubt that the ancient avatara-Buddha and the modern Gautama Buddha are not the same person.
Buddha-avatara has been discussed in various Puranas such as the Linga, Bhavishya, Varaha, Agni, Vayu, Skanda, Vishnu and many others. In the 17th and 18th Chapters of the 3rd Section of Vishnu Purana, Buddha is referred to as Mayamoha. It should be remembered that the Buddha-avatara whose narrations are found in various Puranas and other scriptures, is not the nihilistic Buddha, the son of Suddhodana.