Explanation of the hadith
The Prophet (may Allah's peace and blessings be upon him) said that ‘Abdullāh ibn ‘Umar was a righteous man and encouraged him to perform Qiyām. So, since then, he used to sleep very little at night.
What an excellent man ‘Abdullāh is if only he observes the night prayer
Authentic hadithNarrated by Bukhari & MuslimHadeethEnc #4223
وعن سالم بن عبد الله بن عمر بن الخطاب رضي الله عنهم عن أبيه: أن رسول الله صلى الله عليه وسلم قال: « نِعْمَ الرَّجُلُ عبد الله، لو كان يُصلِّي من الليل» قال سالم: فكان عبد الله بعد ذلك لا يَنامُ من الليل إلا قليلًا.
English translation
Sālim ibn ‘Abdullāh ibn ‘Umar ibn al-Khattāb (may Allah be pleased with him) reported from his father that the Messenger of Allah (may Allah's peace and blessings be upon him) said: "What an excellent man ‘Abdullāh is if only he observes the night prayer." Sālim said: "Since then, ‘Abdullāh would not sleep at night but very little."
Voluntary Prayer