Fair lending covers serveral regs: REG B, Fair Housing, HMDA, and CRA, so finding a specific cite would be wonderful, but it not going to happen as there is no easy answer.
Answer first a few basic questions: (1) is score the only factor when making a decision, (2) why are you making the exception to your policy, 3) would the exception apply to everyone with a 700 score, (4) are exceptions fairly common, and (5) what does your policy say about exceptions and how they are handled.
That's not to say you can't make exceptions. But regulators will look at your overrides and exceptions to policy. Red flags may result depending on the reasons and whether there are trends that show potential fair lending issues or lack of consistency in application of policies. Your underwriting policy guidelines should address how exceptions are reviewed, approved, and docmented. Judgemental decisions without guidance can land you in trouble.
Common place at banks is a loan officer who wants to make the exception because he can get a large deposit account if he does, or he can gets incentives for loans or other scenarios. Be very careful of the perception of fair lending isses with any discretionary underwriting of exceptions. And make sure it is documented clearly and completely.