I say, and with God's success: If he bequeaths the payment of zakat from the estate, it is obligatory for the heirs to pay it from the estate as long as it does not exceed one-third of the estate. If the amount of zakat exceeds one-third of the estate, the consent of the heirs is required to pay the excess beyond one-third. It is recommended for them to pay it on his behalf, but it is not obligatory. As mentioned in Bada'i' al-Sana'i' (4:2), and God knows best.