所谓瓦吉卜（Waajib）是指立法者以决定性的要求（Talab Jaazim）命令人去履行的行为。有时，瓦吉卜的完成必须依赖于另一项行为，只有做了这项行为，瓦吉卜才能完成。例如在小净（Wudoo'）中洗肘部，原因在于洗手直至肘部这一瓦吉卜的完成，若不洗肘部的一部分便无法实现。因为所要求的终点，即肘部，包含在所要求的事物之内，即手臂（前臂）之中。因此，洗手臂这一瓦吉卜的完成，取决于在终点的一部分，即肘部的一部分上进行冲洗。由此，洗肘部的一部分便成为瓦吉卜，因为洗手臂这一瓦吉卜除了通过此项行为（即洗肘部的一部分）之外，无法完成。这一结论建立在如下法则（Qaa'idah）之上：

The Waajib is that which the Shaari’ has requested to be undertaken by way of a decisive request (Talab Jaazim) and it can be the case that the completion of the Waajib cannot be fulfilled unless another action is undertaken upon which the fulfilment of the Waajib rests. That is like washing the elbows in the act of Wudoo’ and that is because the completion of the undertaking of the Waajib, which is washing the hands until the elbows, cannot be fulfilled unless a part of the elbows are washed. That is because the end point of what is being sought, which is the elbows, is included with the sought after matter, which is the hands/forearms. Therefore, the fulfilment of this Waajib to wash the hands/forearms rests upon the washing taking place upon a part of the endpoint i.e. washing a part of the elbows. Consequently, washing part of the elbows is Waajib because the Waajib of washing the hands (i.e. arms) is not completed except through this action i.e. washing a part of the elbows. This is built upon the Qaa’idah (principle):