Fear Allah! اتق الله

The statement said by Allah تعالى to the best of mankind, the Prophet صلى الله عليه وسلم:

﴿يَا أَيُّهَا النَّبِيُّ اتَّقِ اللَّـهَ وَلَا تُطِعِ الْكَافِرِينَ وَالْمُنَافِقِينَ ۗ إِنَّ اللَّـهَ كَانَ عَلِيمًا حَكِيمًا﴾

{O Herald of the Hidden (the Prophet), continue to fear Allah and never listen to the disbelievers and the hypocrites; indeed Allah is All Knowing, Wise.} [Surah al-Ahzab 33:1]

A statement said by one Khalifah to the other. Hazrat Abu Bakr رضي الله عنه, on his death bed, advised Hazrat Umar رضي الله عنه saying:

“Fear Allah O Umar! And know that for Allah there are deeds (which are to be done) in the day which He does not accept in the night; and actions (which are to be done) in the night which He does not accept in the day.”
[Hilyatul Awliyaa and Sifatus Safwah of Ibn al-Jawzee]