Do supplication (du'a) and seeking forgiveness (istighfar) change destiny (qadar), and does frequent istighfar fulfill impossible prayers (du'as), and is there a specific number for istighfar, and is it permissible to seek forgiveness for a stranger, and do the angels say to one who seeks forgiveness for another: "And to you the same"?

Pre-ordainment (Al-Qadar) is Allah's knowledge, inscription, and creation of everything before it occurs. Supplication (Du'a) changes the suspended decree, not the eternal, unalterable one. It is a great means for a servant to attain what they desire, provided the supplicant does not transgress in their supplication.

It is permissible to supplicate for someone you do not know. The virtue of supplicating for believers in their absence has been affirmed, whether it is a general supplication for Muslims or a specific one for someone you do not know.

Seeking forgiveness (Istighfar) is a means to attain all good and to have supplications answered. We do not know what the questioner means by "impossible supplications." If she means what is difficult to obtain among things that Allah customarily answers, then seeking forgiveness is a means to attain it. However, if it falls under transgressing in supplication, then it is not permissible.

There is no specific number for seeking forgiveness, except in instances where the Sunnah has specified a number, such as seeking forgiveness three times after concluding the prayer with Taslim.