What is the ruling on one who says "in sha Allah" (God willing) while not intending to act upon what he said, and does this entail expiation despite not knowing the ruling beforehand?

Whoever says, "I will do such and such, God willing," while intending not to do it, has lied and broken a promise. This person does not sin by this lie if they were ignorant of its ruling. No expiation is required for breaking a promise. Fulfilling a promise is recommended according to the majority of scholars.