‘Abdallah b. Mas'ud reported God’s Messenger as saying, “Let those of you who are sedate and prudent be near me, then those who are next to them (saying it three times), and beware of haphazardness* such as is found in markets.”
God’s Messenger used to touch our shoulders at the prayer and say, “Keep straight; do not be irregular and so have your hearts irregular. Let those of you who are sedate and prudent be near me, then those who are next to them, then those who are next to them." Abu Mas'ud said, “Nowadays you are much more irregular."
Abu Sa'id al-Khudri told that when God’s Messenger saw a tendency among his companions to go to the back he said to them, “Come forward and follow my lead, and let those who come after you follow your lead. People will continue to keep to the back till God will put them at the back.”*
* This has been explained as referring to their being denied God’s grace, or their lacking rank or knowledge. But cf. the tradition from 'A’isha at the end of Section III.