The poem by Minamoto no Toshiyori (1055?-1129?) is from the Kamakura-period imperial poetry anthology Gyokuyo wakashu (Collection of Jeweled Leaves):
Matsukage no utsureru yado no ike nareba
mizunomi tori mo chiyo zo sumubeki
With the beautiful reflection of the shadow of a pine tree in the pond of a mansion, birds that come to the pond to drink should stay forever.