Hadith
The Holy Prophet (saw) says:
 إنمَا فُرِضَتِ الصّلاةُ وأُمِر بِالحَجِّ والطّوافِ وأُشْعِرتِ المَناسِكُ لإقَامَةِ ذِكْرِ اللهِ، فإِذا لم يكُنْ في قَلبِكَ لِلمذكُورِ الّذي هو المَقصُودُ والمُبتَغى عَظَمَةٌ ولا هَيبَةٌ فَما قيمَةُ ذِكْرِك؟
The daily prayer, Hajj, circumambulation, and the other rites are aimed at remembering Allah. But when there is no remembrance of Him in your heart, what value will your oral remembrance have
See Jami'us-Sa'aadat; Vol. 3 p.322