We were deeply saddened / It was a great shock to read / hear of the death of your husband.
You have all my sympathy in this great loss.
We would like to say how sorry we are.
[fml] I would like to assure you of our deepest sympathy in your tragic loss.
lub
We would like to express our sincere condolences.
We are all thinking of you at this time / You are very much in our thoughts. Please let me know if there is anything we can do.

[fml] - formalnie