This has been mentioned in a number of classical books of Islamic history, however it is important to bear in mind that the scholars have made it clear that not everything mentioned in a book of history is authentic. Rather they clearly warned against accepting everything found in books of history.
قَالُوا: وَكَانَ كَثِيرَ التَّزَوُّجِ، وَكَانَ لَا يُفَارِقُهُ أَرْبَعُ حَرَائِرَ، وَكَانَ مِطْلَاقًا مِصْدَاقًا، يقال إنه أحصن سبعين امْرَأَةً
They said, he (Sayidina Hasan) used to marry often, and he always had four wives, and he used to divorce often and paw a lot of dowry. It is said that he married seventy women. (Imam Ibn Katheer, al-Bidayah wa al-Nihayah).
وَكَانَ مِنْكَاحاً مِطْلاَقاً، تزوَّج نَحْواً مِنْ سَبْعِيْنَ امْرَأَةً، وقلَّما كَانَ يُفَارِقُهُ أَرْبَعُ ضَرَائِرَ
He (Sayidina Hasan) used to marry often and divorce often. He married about seventy women, and it was rare for him to have less than four wives. (Imam al-Dhahabi, Siyar A’laam al-Nubalaa).
It is important to note that when they say he had seventy wives, that does not mean at one time. Rather Imam Hasan did not have more than four wives at any time, rather he would marry women and then divorce them, so he could marry others. This was done with complete transparency and without misleading anyone.
In any case, it is not correct to present such information as a matter of fact. Rather we say it is narrated in books of Tareekh (history), which do tend to have the same level of rigour in authentication found in books of Hadith. Therefore, such narrations should be treated as speculative rather than factual.
– Answered by Shaykh Noor ud-deen (04.01.2021)
History books contain problematic narrations
Seerah books are not completely authentic