Hadith 40, 40 Hadith an-Nawawi
On the authority of Abdullah ibn Umar (may Allah be pleased with him), who said:
The Messenger of Allah (peace and blessings of Allah be upon him) took me by the shoulder and said, “Be in this world as though you were a stranger or a wayfarer.”

And Ibn Umar (may Allah be pleased with him) used to say, “In the evening do not expect [to live until] the morning, and in the morning do not expect [to live until] the evening. Take [advantage of] your health before times of sickness, and [take advantage of] your life before your death.” [Al-Bukhari]
عَنْ ابْن عُمَرَ رَضِيَ اللَّهُ عَنْهُمَا قَالَ: أَخَذَ رَسُولُ اللَّهِ صلى الله عليه و سلم بِمَنْكِبِي، وَقَالَ: "كُنْ فِي الدُّنْيَا كَأَنَّك غَرِيبٌ أَوْ عَابِرُ سَبِيلٍ". وَكَانَ ابْنُ عُمَرَ رَضِيَ اللَّهُ عَنْهُمَا يَقُولُ: إذَا أَمْسَيْتَ فَلَا تَنْتَظِرْ الصَّبَاحَ، وَإِذَا أَصْبَحْتَ فَلَا تَنْتَظِرْ الْمَسَاءَ، وَخُذْ مِنْ صِحَّتِك لِمَرَضِك، وَمِنْ حَيَاتِك لِمَوْتِك. 
 [رَوَاهُ الْبُخَارِيُّ].