Tafsir of Al Imran 3:43

وَارْ‌كَعِي مَعَ الرَّ‌اكِعِينَ (and bow down with those who bow) while giving an order to bow down, the imperative has been qualified with the words |"with those who bow|"- but no such qualification appears while giving an order of prostration. This apparently seems to hint that people general¬ly do not observe due concern while making ruk a` (bowing). They tend to bend a little, then resume the standing position (as if in a hurry). This kind of رکوع ruku' (bowing) is closer to standing قیام (qiyam). As said earli¬er, it apparently seems to suggest that Allah Almighty, by mentioning the qualification 'those who bow', has given a model to be followed so that one's bowing in prayer could become similar to those who bow ful¬ly and perfectly as due.