Get binding on source dependency property

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C#

XAML

How do I get hold of a binding on the source, BindingOperations.GetBinding only works on target dependency properties.

[Update]
Let me try to rephrase my problem:

public class Alias : DependencyObject
{
public Int16 Int16
{
get { return (Int16)GetValue(Int16Property); }
set { SetValue(Int16Property, value); }
}
 
public static DependencyProperty Int16Property =
DependencyProperty.Register(
"Int16",
typeof(Int16),
typeof(Alias),
new PropertyMetadata(OnInt16Changed));
 
private static void OnInt16Changed(
DependencyObject d,
DependencyPropertyChangedEventArgs e)
{
var sender = (Alias)d;

BindingExpressionBase binding = BindingOperations.GetBindingExpressionBase(
sender,
Int16Property);
 
var error = new ValidationError(new MyValidationRule(), binding);
Validation.MarkInvalid(binding, error);
}
}
}

The class Alias is a source on a binding, where the target is a UI element. The problem is that BindingOperations.GetBindingExpressionBase doesn't get me the binding since the dependency property Int16Property is the source on the binding, and not the target.

So the question is, how do I get hold of the binding if I know the source property?
[/Update]