Does an expiatory offering for an oath (kaffarat al-qasam) become obligatory for someone who swore that he does not possess wealth, while he possesses less than what the beggar needs?

Swearing falsely is the al-Yamin al-Ghamus (the

perjurious oath), and it is forbidden. Scholars have differed on the necessity of expiation for it; the Hanbalis and Hanafis held that expiation is not required, while the Shafi'is deemed it obligatory. The Malikis provided a detailed view, making it obligatory for oaths concerning the present but not the past. It is more prudent to offer expiation, unless the one who swore was truthful in his intention, in which case there is no sin and no expiation upon him. One must beware of lying in general, and false oaths in particular, and strive to do good to people as much as possible.