Narrated `Abdullah:I used to greet the Prophet (ﷺ) while he was in prayer and he would return my greeting, but when we returned (from Ethiopia) I greeted the Prophet (while he was praying) but he did not return the greeting, and (after finishing the prayer) he said, "In the prayer one is occupied (with a more serious matter)
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“Read in the name of your Lord who created.” 96:1
“My Lord, increase me in knowledge.” 20:114
“So remember Me; I will remember you.” 2:152
“Indeed, with hardship comes ease.” 94:6