Answered by Shaykh Faraz Rabbani
Question: If one passes by a field and plucks some fruit from the trees without asking for permission (because there is no one there to ask), is this considered stealing?
Walaikum assalam wa rahmatullahi wa barakatuh
The Messenger of Allah (peace and blessings be upon him) said, “Nothing is permitted for a Muslim from another’s property except with their willful agreement.” [Related by Ahmad and others]
The general principle is that it is not permitted to take another’s property without permission or agency. [Ibn Abidin, Radd al-Muhtar]
Permission can be explicit or effective. The general customary practice of a land or area establishes effective permission. Thus, if you are sure that the established custom of a particular place is that people don’t mind passersby picking the odd fruit from their trees, then you can do so. If you aren’t sure, it would be impermissible (haram) to pick it up. [ibid; Nablusi/Barkawi, Sharh al-Tariqa al-Muhammadiyya]
And Allah alone gives success.