Al-Biruni a Persian scholar who came to the subcontinent in 1017, wrote this about Sati

 If a wife loses her husband by death, she cannot marry another man. She has only to choose between two things-either to remain a widow as long as she lives or to burn herself; and the latter eventuality is considered the preferable, because as a widow she is ill-treated as long as she lives. As regards the wives of the kings, they are in the habit of burning them, whether they wish it or not, by which they desire to prevent any of them by chance committing something unworthy of the illustrious husband. They make an exception only for women of advanced years and for those who have children, for the son is the responsible protector of his mother.

He wrote this in his book, 'Taḥqīq mā li-l-Hind'.

So they have been practicing sati for at least a thousand years and then they say it was because of Muslims.

 

Al biruni also mentions in his book

1. Indian society was cast-ridden.
2. Several evil prac­tices like child marriage, prohibition of widow marriage, ‘Sati’ existed in the Hindu society.
3. He does not mention the system of dowry but he writes about the 'StreeDhan' which the relatives of girls present to her in-laws.
4. The entire country was divided into small states which occasionally used to quarrel among themselves. These states were jealous of each other and constantly engaged in fights against one another. Malwa, Sindh, Kannauj and Kashmir were prominent states among them.
5. The feeling of nationalism was almost absent.
6. The Hindus of the rural regions worshipped many gods and goddesses.
7. Idol worship was prevalent. Brahmans had the sole privilege of reading the Hindu scriptures. Only the Brahmans had the right to attain salvation.

He even mentions that if a shudra utters a word from vedas, his tongue be cut off.

Brhatsamhita by Varahamihira is a much older and detailed record of sati and jauhar, caste discrimination and segregation, etc. Also lists a few recipes