I think you mean this one:
Dim rng As Range
If Lastrow <> 1 And nr_faktury <> "" Then
Set rng = skoroszyt.Worksheets(nazwa_arkusza).Range(faktury_range).Find(What:=nr_faktury, _
LookAt:=xlWhole, _
LookIn:=xlValues, _
MatchCase:=False)
If Not rng Is Nothing Then
MsgBox "Podany nr faktury zostal podany w fakturze nr" & _
rng.Address & vbNewLine & "Faktura nie zostala zapisana"
Exit Sub
End If
End If
for partial match, change LookAt:=xlWhole
to LookAt:=xlPart