Why is saying "May Allah accept [it from you]" to a person praying considered an innovation (bid'ah), while this supplication is accepted for the pilgrim (Hajj) and the 'Umrah performer without denunciation, even though both are obligatory acts of worship?

The commitment to a Muslim saying to his brother after prayer, "Taqabbal Allah" (May Allah accept [it from you]), as an act of worship is an innovation (bid'ah), because it has not been authentically reported from the Prophet (peace be upon him) nor from his Companions. However, saying it to a pilgrim (Hajj) or an 'Umrah (definition) performer is recommended (mustahabb), and it has been authentically reported from Ibn 'Umar and others that they used to say that to the pilgrim. The Shafi'is have also adopted the view that it is recommended to supplicate for the pilgrim or 'Umrah performer for the acceptance of their Hajj or 'Umrah and for forgiveness.