I read in one of your Fataawa that pronouncing divorce after an invalid marriage does not constitute anything. I was hoping if you could provide some evidence (Hadeeth, etc...) for this as I suffer extremely from doubts as to anything anyone says without concrete evidence. Also can you suggest any remedies for these doubts e.g. how do I know that the thoughts (which are very confusing) are Waswash from Satan.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

You have to know that the evidence may sometimes be from the Book of Allaah or the Sunnah of the Prophet or it may be a consensus of the scholars or a considerable analogy. Divorce after an invalid marriage could be for instance after a temporary marriage, so this kind of divorce is not taken into account. The reason is mentioned in Fatwa: 83843, which is that this divorce is not appropriate; divorcing (in such a case) is like divorcing a woman who is not one's wife in principle. It is confirmed that the Prophet said: "There is no vow for the child of Aadam in what he does not possess, and he cannot free a slave whom he does not possess or divorce a woman who is not his own wife." [At-Tirmithi]

However, if the marriage is considerably differed about among the scholars whether or not it is valid, like the marriage without the (the presence or consent of the) guardian of the bride, then divorce in such a case is considered because of those [scholars] who consider it to be correct. Some scholars even consider that such a divorce is irrevocable.

Finally, you have to know that asking for an evidence in itself is not blameworthy, however, a person who does not clearly understand the evidences, has to ask the trustworthy religious and knowledgeable scholars and that would be sufficient for him. So, if this is what you feel but you have whispers that prevent you from acting according to the Fatwa or to believe in it, then this is really a kind of whisper (i.e. from the devil). To treat this, you should seek refuge in Allaah from the accursed devil, supplicate Him as much as possible, and act according to the Fatwa if necessary without taking these whispers into consideration.   

Allaah knows best.