How to work with label'om specified in .xaml code in c# code (xamarin)?

Question

C++ / C#

In the xaml code, I define a label named l:

<Label Text="a" x:Name="l" HorizontalOptions="Center" VerticalOptions="CenterAndExpand" />

And then in the c# code in the procedure, I need to change its text: Error: "The name "l" does not exist in the current context. How to be?
l.Text = "b";