«كان إذا مر بآية خوف تعوذ وإذا مر بآية رحمة سأل وإذا مر بآية فيها تنزيه الله سبح»
It was the practice of the Prophet (peace and blessings be upon him):
"When, during recitation, he (peace and blessings be upon him) passed a verse that spoke of the fear of punishment, he would seek refuge; when he passed a verse of mercy, he would ask Allah (for it); and when he passed a verse that declared Allah's transcendence, he would glorify Him."
Hadith Referenceصحیح الجامع الصغیر / حرف الكاف / 4782