With Selection.Validation
.Delete
.Add Type:=xlValidateTextLength, AlertStyle:=xlValidAlertStop, _
Operator:=xlEqual, Formula1:="4"
.IgnoreBlank = True
.InCellDropdown = True
.InputTitle = ""
.ErrorTitle = "Erreur"
.InputMessage = ""
.ErrorMessage = "Veuillez saisir 4 chiffres."
.ShowInput = True
.ShowError = True
End With