Abdul Wahab bin Bakht Makki (may Allah have mercy on him) said: When there is fighting, if you have the strength, then perform the prayer standing; otherwise, while riding. If that is also not possible, then say the takbeer. If even that is not possible, then at least keep the intention of prayer in your heart.
Hadith Referenceسنن سعید بن منصور / كتاب الجهاد / 3693
Hadith Takhrij«أخرجه سعيد بن منصور فى «سننه» ترقيم الدرالسلفية برقم:، 413، 2516»