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.
The meaning of blessing is goodness and prosperity [growing and flourishing]. We have not come across any statement of the scholars regarding wishing blessings for a disbeliever to preserve his wealth. Nevertheless, it appears – and Allaah knows best – that this is included in supplicating for him regarding the goodness of this worldly life; a matter that has been permitted by the scholars. An-Nawawi said in Kitaab Al-Athkaar (Chapter: What a Muslim says to a Thimmi [Jew or Christian living under the care of the Muslim state] if the latter does an act of goodness to him), “You should know that it is not permissible to supplicate for him with forgiveness and other things that are not said to the non-Muslims, but it is permissible to supplicate for him for guidance, good health, wellbeing, and the like.”
It was reported in the book of Ibn As-Sunni from Anas that he said, “The Prophet sought water to drink, and a Jew gave him water, and the Prophet said to him, 'May Allaah beautify you.' This man never got gray hair until he died.” This hadeeth was considered to be weak by some scholars. But there is the hadeeth by Abu Sa'eed Al-Khudri about the person who was bitten that says that the Companions performed Ruqyah (healing through Quranic recitation and supplications) on the leader of the neighborhood, who was a disbeliever. Ruqyah is a kind of supplication.
We conclude from this that it is permissible to supplicate and seek blessings for a non-Muslim who is at peace with the Muslims (not hostile towards them and fighting them). However, it is preferred to do this for a person about whom it is expected to soften his heart towards Islam.
Allaah knows best.