Is it true that some Companions practiced masturbation during battles, as mentioned in the book "Fiqh Al-Sunnah," and to what extent is it valid to base rulings on this statement?

Masturbation is forbidden, according to the preponderant opinion of the scholars. What was mentioned about some of the Salaf allowing it was in the category of "permission for it" when there is a necessity, such as one who fears fornication or fears illness if they do not do it. As for without necessity, no one is known to have permitted it.