I know someone who does not believe in any Hadeeth that he doesn't understand or that seems to contradict the Qur'an even if they are Saheeh. Like the Hadeeth of Sulaymaan sleeping with 90 wives in one night, etc.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

In fact, Sunnah (Prophetic narrations) is also a revelation from Allaah like the Qur'an. Allaah says (which means): {…Nor does he speak from [his own] inclination. It is not but a revelation revealed.}[53:3-4].

So, Sunnah is used as a legal proof in Islam as the Qur'an is used. Allaah says (which means): {And whatever the Messenger has given you—take; and what he has forbidden you—refrain from. And fear Allaah; indeed, Allaah is severe in penalty.}[59:7].

The Prophet said: "The time is about to come when a man lying on his couch will narrate one of my narrations then say: 'between you and us (as a judge) is the Book of Allaah (Qur'an). What we find in it to be permissible, we will deem it permissible, and what we find in it to be prohibited, we will deem it prohibited'. Beware! What the Prophet has prohibited is absolutely as Allaah has prohibited (i.e. holds the same weight)." [Abu Daawood]

If a Muslim notices contradiction between two texts and cannot make consistency between them, he has to entrust its knowledge to Allaah and should ask the knowledgeable people.

The narration that Sulaymaan had slept with his ninety wives in a night, is reported by Imaams Al-Bukhari and Muslim, so it is a sound and authentic narration. Sulaymaan was a Prophet and infallible and had been granted a separate divine law. Therefore, we cannot compare a divine law granted to a Prophet with another divine law granted to another Prophet.

If it is said that marrying more than four wives is not allowed as mentioned in the Qur'an, as Allaah says (which means): {…then marry those that please you of [other] women, two or three or four...}[4:3]. Then the answer is:

First, this ruling does not contradict the narration because all the Prophets had some peculiarities, that common people could not share. So, it might be the peculiarity of the Prophet Sulaymaan, my Allaah exalt his mention, to marry up to ninety women as it was the peculiarity of the Prophet Mohammad to marry more than four wives.

Second, as we have mentioned that the divine laws that were granted to the Prophets were varied from one Prophet to another in the offshoots though they were same in basic matters. The mentioned matter can be one of those matters, which is varied from one divine law to another one.

If it is meant that the narration which approves sleeping with more than ninety women in a night does not appeal to mind (i.e. does not make sense), the answer is that it is not impossible. The Prophets were granted such a power and strength to prove their perfect manhood, sound health and ideal heroism that is not given to any common person. Moreover, a sound and clear narration cannot be denied based on rationalism.

Allaah knows best.