Adam Clarke on Genesis 31:50

No man is with us - Though all were present at the sacrifice offered, yet it appears that in making the contract Jacob and Laban withdrew, and transacted the business in private, calling on God to witness it.

Jacob had already four wives; but Laban feared that he might take others, whose children would naturally come in for a share of the inheritance to the prejudice of his daughters and grandchildren. Though the Koran allows a man to have four wives if he can maintain them, yet we learn that in many cases where a man takes a wife, the parents or relatives of the woman stipulate that the man is not to take another during the lifetime of that one whom he now espouses; and notwithstanding the permission of the Koran, he is obliged to fulfill this agreement.