Don’t Make Conditions with G-d

In response to someone who asked for a blessing for his daughter and son-in-law to have children, and said that when it would be fulfilled he would donate generously to the Chabad Yeshivah Tomchei Temimim:

...why should he get into conditions with G-d? It is known that our Sages say that one who gives a “Sela” to Tzedakah so that etc. is a completely righteous person, but nevertheless they do not say a condition that he will give after the request will be fulfilled. Certainly he also understands on his own that when there is a question, Who is more reliable – certainly G-d is most trustworthy and also all-capable...

(See letter of the Lubavitcher Rebbe King Moshiach Shlita, Igros Kodesh vol. 5, pg. 147)