I saw no reason _____ we should get up early.

For

Why

That

How

The correct phrase is "I saw no reason why we should get up early".

میں نے کوئی وجہ نہیں دیکھی کہ ہمیں جلدی کیوں اٹھنا چاہئے۔

As "why" introduces the reasoning behind the statement.