The Messenger of Allah ﷺ used to supplicate during the prayer, after saying "Allah hears the one who praises Him, our Lord, and to You belongs all praise." Then, while still standing before going into prostration, he would say, "Allah, save Walid bin Walid, Salama bin Hisham, Ayyash bin Abu Rabia, and the oppressed believers. Allah, tighten Your grip upon Mudar, and make it for them like the years of Yusuf." Then he would say, "Allah is the greatest," and prostrate. The open territory of Mudar at that time was in opposition to the Messenger of Allah ﷺ.
أخبرنا عمرو بن عثمان قال حدثنا بقية عن ابن أبي حمزة قال حدثني محمد قال حدثني سعيد بن المسيب وأبو سلمة بن عبد الرحمن أن
أن رسول الله ﷺ كان يدعو في الصلاة حين يقول سمع الله لمن حمده ربنا ولك الحمد ثم يقول وهو قائم قبل أن يسجد اللهم أنج الوليد بن الوليد وسلمة بن هشام وعياش بن أبي ربيعة والمستضعفين من المؤمنين اللهم اشدد وطأتك على مضر واجعلها عليهم كسني يوسف ثم يقول الله أكبر فيسجد وضاحية مضر يومئذ مخالفون لرسول الله ﷺ
Bukhari transmitted it in the tafsir of Al Imran, chapter "You have no part in the matter," hadith 4560, and Muslim in the Book of Masajid, chapter on the recommendation of qunut in all prayers, and so on, hadith 675, from the hadith of Muhammad bin Muslim Zuhri, through the same chain. It is also found in the Kubra, hadith 661.