Is it permissible to say, "I put my trust in Allah" (tawakkaltu 'ala Allah) when undertaking any matter, and is it sufficient to say it once or three times?

Reliance on Allah is a great act of worship of the heart, and it is prescribed in every matter, for the believer cannot do without Allah's help. Reliance is primarily an act of the heart, not merely a verbal statement. However, saying "I have relied upon Allah" when leaving one's home is a way of bringing to mind this reliance, and it has been established in the Sunnah. So, upon leaving the house, one says: "In the name of Allah, I have relied upon Allah, there is no might and no power except with Allah." It is then said: "You have been guided, sufficed, and protected." There is no harm in saying "I have relied upon Allah" when going out for any matter. As for saying it before every action, it has not been established as a specific Sunnah, but if it is said as a general supplication, remembrance, and seeking help from Allah, then there is no harm.