Explained by al-‘Allaamah Muhammad Ibn Saalih al-‘Uthaymeen [d. 1421H]

If you have reached the evening, then do not say: ‘I will remain until the morning.’ How many people have reached the evening without reaching the morning? And likewise, his saying, ‘And if you reach the morning, then do not wait for the evening.’ And how many people reached the morning without reaching the evening? And Ibn ‘Umar’s intent regarding this is that mankind seize the opportunity to do righteous deeds so that he does not lose his time in this world whilst he does not realise it.

 On the authority of Ibn ‘Umar (radiyallaahu ‘anhumaa) who said, ‘The Messenger of Allaah (sallallaahu ‘alayhi wa sallam) took me by my shoulders and said: ‘Be in this world as if you are a stranger or a wayfarer.’’

And Ibn ‘Umar (radiyallaahu ‘anhumaa) used to say: ‘If you reach the evening, then do no wait for the morning, and if you reach the morning, then do not wait for the evening. And take (advantage of) your health before times of sickness, and take (advantage of) your life before your death.’