The Gemara relates that Reb Chalafta would help his father, even before his father asked for something. He was rewarded (Yeshayah 65:24) אענה ואני יקרא טרם והיה, that Hashem gave him what he wanted, even before he asked for it.
It states (Tehillim 45:17), בניך יהיו אבותיך תחת הארץ בכל שרים תשיתמו, "In place of your forefathers will be your sons; you shall appoint them princes throughout the land." The Midrash (Mishnas Reb Eliezer) writes that אבותיך תחת means in the merit of kibud av v'em, בניך יהיו, you will merit children. Lest you think they will be ordinary children, therefore the pasuk adds, הארץ בכל שרים תשיתמו, that the parents will merit exceptional children.
The Pele Yoetz writes that in the merit of his toil [to perform kibud av v'em], he will merit good children, and if it were only for that reward, it would be worth striving with all his strength to perform this mitzvah.
It states (Bereishis 27:31), לאביו ויבא, and these words can be read forward and backwards, which hints that when one does kibud av v'em, it will come back to him because his children will honor him as well.
Tana d'Bei Eliyahu (Raba ch.26) states, "Whoever desires longevity, wealth, or honor in this world and the next world should do the will of his father in heaven and the will of his father and mother."
Rabbeinu b'Chayei (Kad HaKemech) writes, "It is clear that people are rewarded in this world for doing kibud av v'em, or that they experience tranquility and success with everything they do."
The sefer Meah She'arim (Shar 16) writes, "Whoever keeps this mitzvah, nothing bad will happen to him. The One Who rewards is trusted that He will send malachim before him to protect him."
