Is it permissible to perform the funeral prayer without ablution due to necessity, and then the worshiper performs ablution after finishing it?

The funeral prayer (Salat al-Janazah) is governed by the rulings of prayer. Therefore, purity from impurities (khabath) and ritual impurity (hadath) is required for it, as well as facing the Qiblah, and covering the 'awrah. In cases of necessity and unavailability of water, tayammum (dry ablution) is permissible by striking the hands on the earth and wiping the face and palms, according to the Almighty's saying: (Then perform tayammum with pure earth and wipe therewith your faces and hands). A prayer performed in the prescribed manner is not to be repeated.