It is narrated from Nafi‘ that when Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) would finish the fasts of Ramadan and intended to perform Hajj, he would not cut the hair of his head or beard until he had performed Hajj.
Imam Malik (may Allah have mercy on him) said: This matter is not obligatory upon all people.

It is narrated from Hazrat Nafi that when Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) would shave his head during Hajj or Umrah, he would also trim his beard and moustache.

It is narrated from Rabi'ah bin Abi Abdur Rahman that a man came to Qasim bin Muhammad and said, "I performed the Tawaf al-Ifadah and my wife also performed the Tawaf al-Ifadah. Then I went towards a valley to have intercourse with my wife. She said, 'I have not yet cut my hair.' So I cut her hair with my teeth and then had intercourse with her." Qasim bin Muhammad laughed and said, "Order your wife to cut her hair with scissors."

Imam Malik, may Allah have mercy on him, said that in my view, it is preferable that the man offers one sacrifice, because Sayyiduna Abdullah bin Abbas, may Allah be pleased with them both, said: Whoever forgets any pillar from the pillars of Hajj, then he should offer one sacrifice.

Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) met one of his relatives whose name was Mujbir (he was the nephew of Sayyiduna Abdullah bin Umar, the son of Sayyiduna Abdur Rahman bin Umar, may Allah be pleased with them both). He had performed the Tawaf al-Ifadah but, out of ignorance, had neither shaved his head nor shortened his hair. So Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) instructed him to return, shave or shorten his hair, and then repeat the Tawaf az-Ziyarah.

Imam Malik, may Allah have mercy on him, was informed that Salim bin Abdullah bin Umar, when he intended to enter into ihram, would call for scissors and trim his moustache and beard before mounting his ride and before saying the talbiyah, after tying the ihram.