Adam Clarke on Mark 6:44

Were about five thousand - ὡσει, about, is omitted by a great majority of the best MSS. and by the principal versions. It is wanting in several editions: Bengel, Wetstein, and Griesbach, leave it out of the text. It is omitted by some in the parallel place, Mat 14:21, but it stands without any variation in Luk 9:14, and Joh 6:10. This miracle is mentioned by all the four evangelists. It is one of the most astonishing that Christ has wrought. It is a miracle which could not be counterfeited, and a full proof of the divinity of Christ.