Halakhah zu Amos 4:12

The Sages teach that one who needs to use the bathroom, be it to urinate or to defecate, may not pray (Berakhot 23a). There are two reasons for this: 1. The need for relief is likely to disrupt one’s kavana (Rambam); and 2. It is not proper to come to pray before God when the body is made repulsive by the excrement inside it (Hagahot Maimoniyot). Even if one is uncertain as to whether or not she needs to use the bathroom, the Sages say that le-khatḥila one should use the bathroom (Berakhot 15a). The Sages support their statement with the verse (Amos 4:12), “Israel, prepare to meet your God.” It is also written: “Guard your foot when you go to the House of God” (Kohelet 4:17), which they interpret to mean that one should ensure that she does not need to relieve herself when she gets up to pray.

If one urinated and did not brush off [any drops of urine with his hands] - even though he must recite Asher Yatzar, washing his hands is only necessary for [the sake of] cleanliness/hygiene or because of the notion of "Hikkon" (Amos 4:12) (i.e. preparation for the proper davening mindset).

It is written: "Prepare to meet your God, O Israel."¹Amos 4:12. Preparing yourself before Hashem, Blessed is He, means that you should dress yourself in the same type of respectful clothing when you pray, as you would when meeting a high official. Even if you pray privately in your home you should dress properly. In those places where the custom is to wear a special sash [during prayers], it is forbidden to pray until you gird yourself [with such a sash].

“Bless the Lord, O my soul; and all that is within me, bless His holy name” (Ps. 103:1). The insides of a man, even his intestines need to bless the Lord.¹Berakoth 25a. Therefore he must examine himself well when he sets to pray,²Ibid., 23a.
/3/ The Zohar, ed. Soncino, V, 326; also Shabbath 104a. because it is not fit to bless Him while bringing a belly filled with excrement before the Holy One, blessed be He. He needs to shake his entire body during prayer, as it is written, “All mine bones shall sing, Lord, Who is like unto Thee” (Ps. 35:10). It is written, “Guard thy foot when thou goest to the house of God” (Eccl. 4:17), that your feet be not soiled.⁴Berakoth 23a. And it is written “prepare to meet thy God O Israel” (Amos 4:12).⁵Ibid., 15a. When a man appears before a king of flesh and blood he does not come attired as he would for the street, he covers himself, and stands before him with awe, fear and dignity; we who go before the Lord of all the earth, blessed be His name, all the more do we need to cover ourselves and stand before Him with awe and fear.⁶Shabbath 10a. Woe to those who delay covering themselves but from Sabbath to Sabbath so that people not laugh at them.⁷They go uncovered during the week. They do not consider that perhaps they might die and be unable to give honor to Him who gave His own garment, concerning which it is written, “His raiment was as white snow” (Dan. 7:9). Concerning these people and those similar to them it is said, the wicked may prepare it but the righteous shall put it on. (Job 27:17)

One needs to wear a belt at the time of prayer, even if he is wearing pants, such that his heart does not "see" his nakedness, because of הכון/prepare ("Prepare to meet your God, O Israel" (Amos 4:12)). But [regarding] the rest of the blessings, it is permitted to bless them without a belt, so long as one is wearing pants. Rem"a: and one's heart does not see the nakedness (Ran, First Chapter of Shabbat and the Rosh, Chapter "ha-Ro-eh", and Hagahot Maimoni on Tefillah Chapter 5)