Abu Darda (RA) narrated that Rasool Allah (PBUH) said,

Should I not tell you of such a thing which are the best and purest deeds in the court of your Lord, high in ranks, better for you then spending gold and silver in Allah’s path, and better than slaying the neck of the enemy during war?

The Sahaba said, Yes, Oh Rasool Allah!
He said,

It is Zikr of Allah

— Tirmizi

So Brothers and Sisters, We should keep on doing Zikr-ullah when we are free, or even we can recite

• Subhan Allah
• Alhamdolillah
• La elhah el-Allah
• Allah-o-Akbar

for 1,2,3,10,20,30 times when we found gap of 5-10 minutes.

Jazak Allah