Sayyiduna Abu Umamah (may Allah be pleased with him) narrates this saying of the Prophet (peace and blessings be upon him): "Whoever invites you, respond to him! (that is, accept the invitation)."
Al-Tabarani recorded it in al-Mu'jam al-Kabir; its chain contains a narrator, Muhammad bin Ubaydullah al-Arzami, and he is da'if (weak).