Hadith 4:575
Ibn Fudayl narrated to us, from Layth, from Mujahid, who said: When Ibn Umar was invited to a meal while he was fasting, he would accept. When they brought the table and the food was upon it, he would extend his hand and then say, "Take [it], in the name of Allah." Then, when the people reached out [to eat], he would withdraw his hand.
حدثنا بن فضيل عن ليث عن مجاهد قال كان بن عمر إذا دعي إلى طعام وهو صائم أجاب فإذا جاؤوا بالمائدة وعليها الطعام مد يده ثم قال خذوا بسم الله فإذا أهوى القوم كف يده