I think it should be like this:
CREATE TABLE doctor_schedule (
doctor_id int(11) NOT NULL,
attention_time_slot_id int(11) NOT NULL,
available tinyint(1) NOT NULL DEFAULT '1',
date date NOT NULL,
CONSTRAINT pk_doc_schedule PRIMARY KEY (doctor_id,attention_time_slot_id,date),
CONSTRAINT fk_ds_doctor FOREIGN KEY (doctor_id) REFERENCES doctor (id),
CONSTRAINT fk_ds_attention FOREIGN KEY (attention_time_slot_id) REFERENCES attention_time_slot (id)
)
Keep in mind that the types of foreign keys must be of the same type and same name.