“I would like to ask you a favour” vs. “I would like to ask you for a favour”

Question

Which form is to be preferred?

• I would like to ask you a favour.
• I would like to ask you for a favour.

Answer 1

According to this Google NGram, all of the following forms are in use:

• ask you a favo(u)r
• ask you for a favo(u)r

As you can see, the forms without the preposition for are more common (with "ask you a favor" generating the highest results). In common use, one may conclude that this is the preferred form.

Answer 2

I would say the former is preferred/more common in colloquial/spoken English. The latter is not incorrect but used less often.

Answer 3

BBC Learning English uses just the former expression for asking a favour.

Answer 4

Compare it with "Asking a lunch" and "Asking for a lunch" Here, "lunch" is not the actual thing which is being asked; and that's why it should be "Asking for a lunch"

But in case of favour, it's the "favour" which is directly being asked.

Similarly, you can also compare 1. Asking a date 2. Asking for a date

So the correct usage is: "I would like to ask you a favour"