Praised be allah.
Ibn Al-Qayyim has written a very useful book on Islamic rules concerning newborns. It is called Tuhfat Al-Maudûd fi Ahkâm Al-Maulûd. There is a detailed chapter on circumcision and its rules. The following is a summary of it with additional comments from some scholars.

1. The meaning of circumcision (Khitân)
Khitân as a noun describes the work of the one who performs a circumcision (Khâtin). It is also used to specify the place of circumcision, as in the hadith, "When the two circumcised parts (al-Khitânân) touch, ghusl becomes necessary."

2. The circumcision is the sunnah of Ibrahim and the prophets after him
Al-Bukhaari (No. 629Cool and Muslim (2370)), from Abu Hurairah (ra), said that the Messenger of Allaah (ass) said, "Ibrahim (as) performed circumcision when he was eighty years old, and he did The ax was used for that. "

The ax (Al-Qadûm) is the tool of a carpenter. It is also said that Al-Qadûm is a place in Syria.
Al-Hafiz Ibn Hajar said, "The closest thing to the hadeeth is to the tool. Abu Ya'la narrated by Ali ibn Rabâh: "Ibrâhîm was commanded to circumcise himself. He carried her through with an ax, causing him great pain. Then Allaah revealed to him the words, "You hurried to do it before We told you which tool to use." He replied, "Oh Lord, I did not want to delay the execution of your order."

Ibn Al-Qayyim said, "The circumcision was one of the trials of Allaah for Ibrahim, his chosen friend. He passed with flying colors, and so Allaah made him a leader for humanity. It is said that he was the first warrant to be circumcised as stated above. In both Sahîh works it is said that he performed circumcision at the age of 80 years. According to him, circumcision became his practice among the Messengers and their followers, even the Messiah. He was circumcised and the Christians confirmed this without denying it. Likewise, they confess that he was forbidden to eat pork. "(Tuhfat Al-Maulûd, pages 158-159).

However, the scholars differ as to whether circumcision is compulsory or recommended.

Shaykh Ibn 'Uhtaimin said: "The most correct opinion is that it is a duty for men. Circumcision in the case of men serves a purpose related to a condition for prayer, namely the state of purity. Because when urine exits the urethra, part of it collects under the foreskin, which can cause infection by physical movement of the man. And when the foreskin is squeezed, a few drops of urine come out, causing najāsah (impurity). Here it is about perfecting oneself and not about avoiding something harmful. "(Asch-Sharh Al-Mumti', 1 / 133-134).

That was also the view of Imam Ahmad. Ibn Qudamah said in Al-Mughni (1/115): "Circumcision is compulsory for men."

3. How the circumcision is done
Ibn Al-Qayyim said: Abu Al-Barakât wrote in his book Al-Ghâyah: "In circumcision, the man's skin is removed from the tip of the penis (foreskin). If he just removes most of them, that's fine. Al-Khallah said in Jāmi, "What is removed in the circumcision: Muhammad ibn Al-Husain told me that Fadl ibn Ziyâd told them," When Ahmad was asked how much circumcision should be done, he answered, "Until the Acorn becomes visible. "

Ibn As-Sabbâgh wrote in Ash-Shamil: "The man must completely remove the skin at the tip of the penis until the glans becomes fully visible."
An-Nawawi said, "The best known view, which is also the correct one, is that everything that covers the glans must be removed." (Al-Majmû, 1/351).

In summary, in men, the entire skin on the tip of the penis should be removed.

4. The wisdom behind circumcision
Men can not possibly keep their urine completely clean unless they are circumcised, because some drops collect under the foreskin and you can never be sure that something is not dripping and contaminating your clothes and body. Therefore'Abdullah ibn 'Abbas was very strict on the question of circumcision. Imâm Ahmad said:'Ibn Abbâs was very tough on this matter. It is said by him that there is no Hajj and prayer for him, i. if someone is not circumcised, his Hajj and his prayer are invalid. "(Al-Mughni, 1/115).