Identify duplicate values with MsgBox - excel

Question

I have written VBA code to find the duplicate value and bulk upload the data to another sheet.
If any duplicate in A, B, C Columns I need a message box, and to cancel the bulk upload.
Example of my columns - marked in red are duplicate values:
Option Explicit
Private Sub CommandButton1_Click()
Dim rng As Range
Dim l As Long, r As Long, msg As String
Dim lRow, lRow1 As Long
Application.ScreenUpdating = False
l = Range("A" & Rows.Count).End(xlUp).Row
For r = 2 To l
If Evaluate("COUNTIFS(A:A,A" & r & ",B:B,B" & r & ",C:C,C" & r & ")") > 1 Then msg = msg & vbCr & r
Next
MsgBox msg, vbInformation, "DUPLICATE ROWS"
Exit Sub
lRow = [Sheet2].Cells(Rows.Count, 1).End(xlUp).Row
lRow1 = [Sheet3].Cells(Rows.Count, 1).End(xlUp).Row + 1
[Sheet2].Range("A4:N" & lRow).Copy
[Sheet3].Range("A" & lRow1).PasteSpecial xlPasteValues
Application.CutCopyMode = False
Sheet3.Select
[Sheet3].Range("A1").Select
Sheet2.Select
[Sheet2].Range("A1").Select
End Sub

Answer 1

Something like this should work fine:
For r = 2 To l
If Evaluate("COUNTIFS(A:A,A" & r & ",B:B,B" & r & ",C:C,C" & r & ")") > 1 Then
msg = msg & vbCr & r
End If
Next r
If Len(msg) > 0 Then
MsgBox msg, vbInformation, "DUPLICATE ROWS"
Exit Sub
End If

Answer 2

Extended Formula evaluation without loops
Extending on Tim's row-wise formula evaluation a couple of tips:
Fully qualify your range references; without explicit indications VBA assumes the active sheet, which needn't be the one you have in mind.
Execute a worksheet-related evaluation for the same reason; doing so it suffices here to indicate e.g. "A:A" instead of inserting a sheet prefix "Sheet1!..." each time.
Example procedure
Option Explicit ' force declaration of variables on top of code module
Sub IdentifyDuplicateRows()
With Sheet1 ' using the project's Sheet Code(Name)
'1. get last row & build formula
Dim l As Long
l = .Range("A" & Rows.Count).End(xlUp).Row
Dim myFormula As String
myFormula = "=IF(COUNTIFS(A:A,A2:A" & l & ",B:B,B2:B" & l & ",C:C,C2:C" & l & ")>1,""Duplicate Row "" & Row(A2:A" & l & "),"""")"
'2. get results & write to target
Dim results As Variant
results = .Evaluate(myFormula) ' note the "."-prefix!
With .Range("D2").Resize(UBound(results))
.Value = results 'write results to target
End With
'3. optional additional MsgBox info (see below)
' ...
End With
End Sub
Note to optional message box info
If you prefer a further info via message box you could insert the following block before End With:
'3. optional display in message box
'filter only elements containing "Dup" (change to flat & eventually 0-based array)
results = Application.Transpose(results)
results = Filter(results, "Dup") ' omitted default argument Include:=True
'count duplicate rows and display message
Dim cnt As Long
cnt = UBound(results) + 1
MsgBox Join(results, vbNewLine), vbInformation, cnt & " Duplicate Rows"