It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) said: "When any of you is invited, and he comes along with the inviter, then this is permission for him."
Hadith Referenceالادب المفرد / كتاب الاستئذان / 1075
Hadith Gradingالألبانی:صحيح
Hadith Takhrij«صحيح : أخرجه أبوداؤد ، كتاب الأدب : 5190 و رواه أحمد : 533/2 من حديث سعيد بن أبى عروية به»