The Quran

قُل هَل تَرَبَّصونَ بِنا إِلّا إِحدَى الحُسنَيَينِ ۖ وَنَحنُ نَتَرَبَّصُ بِكُم أَن يُصيبَكُمُ اللَّهُ بِعَذابٍ مِن عِندِهِ أَو بِأَيدينا ۖ فَتَرَبَّصوا إِنّا مَعَكُم مُتَرَبِّصونَ

Muhammad Asad

Say: "Are you, perchance, hopefully waiting for something [bad] to happen to us - [the while nothing can happen to us] save one of the two best things?¹ But as far as you are concerned, we are hopefully waiting for God to inflict chastisement upon you, [either] from Himself² or by our hands! Wait, then, hopefully; behold, we shall hopefully wait with you!"

I.e., either victory or martyrdom in God's cause. The verb tarabbasa has usually the connotation of waiting with expectancy, and is, therefore, most suitably rendered as "he hopefully waited".
Sc., in the life to come.