[The Amount to Be Given to a Poor Person from Zakat]

Answer—and Allah is the Granter of success: He is given according to his need; likewise, the stranded wayfarer is given what will enable him to reach his homeland; likewise, the insolvent debtor is given what will settle his debt; and likewise, the combatant in the path of Allah is given what he needs for jihad.
It is permissible to give each of these according to the measure of the need—even if it reaches the nisab or exceeds it—for zakat was legislated and made obligatory for them on account of their need and to fill their lack; thus they are given what will fill that.
This is the madhhab of many scholars from among the People of the House (Ahl al-Bayt) and others. Al-Hādī Yaḥyā b. al-Ḥusayn—may Allah have mercy on him—and those of the madhhab who follow him said: The poor person does not complete a nisab, and it is not permissible for him to take a full nisab in a single payment, nor that which completes a nisab. This view is the more precautionary.
Source : Min Thimār al-ʿIlm wa al-Ḥikmah vol.1