Pseudo-Chrysostom
Catena Aurea · Matthäusevangelium 6
And when thou prayest, thou shalt not be as the hypocrites are; for they love to pray standing in the synagogues and in the corners of the streets, that they may be seen of men. Verily I say unto you, They have their reward. But thou, when thou prayest, enter into thy closet, and when thou hast shut thy door, pray to thy Father which is in secret; and thy Father which seeth in secret shall reward thee openly.
He forbids us to pray in an assembly with the intent of being seen of that assembly, as He adds, that they may be seen of men. He that prays therefore should do nothing singular that might attract notice; as crying out, striking his breast, or reaching forth his hands.